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Microchip Gas Chromatography Columns, Interfacing and Performance
Abstract
Almost four decades of investigations have opened up many avenues to explore the production and utilization of planar (i.e., microchip) gas chromatographic columns. However, there remain many practical constraints that limit their widespread commercialization and use. The main challenges arise from non-ideal column geometries, dead volume issues and inadequate interfacing technologies, which all affect both column performance and range of applications. This review reflects back over the years on the extensive developments in the field, with the goal to stimulate future creative approaches and increased efforts to accelerate microchip gas chromatography development toward reaching its full potential.
... So far, applications of chip-GC have mainly been restricted to the analysis of VOCs due to the limited upper-temperature range (~200°C). For example, silicon, glass, and adhesives that are frequently used for fabrication have mismatching thermal expansion coefficients, which leads to cracking and leaking after thermal cycling (Ghosh et al., 2018). GC methods for analyzing methylated fatty acids and polycyclic aromatic hydrocarbons (PAHs) almost always employ temperatures above 200°C, or even 300°C. ...
... GC methods for analyzing methylated fatty acids and polycyclic aromatic hydrocarbons (PAHs) almost always employ temperatures above 200°C, or even 300°C. There is a vast literature covering fundamental research to improve the upper-temperature limit of microchip GC (Ghosh et al., 2018). Among various approaches, stainless steel microchip GC columns appear particularly promising due to their high thermal conductivity and compatibility with high operating temperatures up to 350°C (Ghosh et al., 2019). ...
... Despite all the recent development in the miniaturization of GC, the engineering of connectors and interfaces are still lagging behind the individual components, such as, those between chip columns, sample introduction sub-systems, and detectors (Ghosh et al., 2018). These connections must be compatible with the high temperature of GC for biosignature analysis and maintain the separation's peak fidelity. ...
The search for life in Solar System bodies such as Mars and Ocean Worlds (e.g., Europa and Enceladus) is an ongoing and high-priority endeavor in space science, even ∼ five decades after the first life detection mission at Mars performed by the twin Viking landers. However, the in situ detection of biosignatures remains highly challenging, both scientifically and technically. New instruments are being developed for detecting extinct or extant life on Mars and Ocean Worlds due to new technology and fabrication techniques. These instruments are becoming increasingly capable of both detecting and identifying in situ organic biosignatures that are indicative of life and will play a pivotal role in the search for evidence of life through robotic lander missions. This review article gives an overview of techniques used for space missions (gas chromatography, mass spectrometry, and spectroscopy), the further ongoing developments of these techniques, and ion mobility spectrometry. In addition, current developments of techniques used in the next-generation instruments for organic biosignature detection are reviewed; these include capillary electrophoresis, liquid chromatography, biosensors (primarily immunoassays), and nanopore sensing; whereas microscopy, biological assays, and isotope analysis are beyond the scope of this paper and are not covered.
... There are a couple of the breath detection technologies at present, gas chromatography (GC)-mass spectrum (MS) and electronic nose are often applied. The GC-MS techniques can realize high detection accuracy and have low detection limit of tens to hundreds ppb, while the large volume and high power consumption hinders its use in point-of-care testing (POCT) [15]. Electronic nose is portable with fast response, but the cross-sensitivity among the sensors decreases detection accuracy [16]. ...
... The relating researches mainly focus on four aspects, such as the fabrication process [22,23], the layout of column [24], the structure [25,26] and the stationary phase. There are many kinds of stationary phases for GC and PDMS is the most common used materials [15]. In recent years, various new kinds of stationary phase materials have shown good chromatographic properties, such as metal organic framework [27], ionic liquids (ILs) [28,29] and graphene [30]. ...
... Surface treatment of the column is vital to obtain better separation performance based on previous experience of open tubular columns [15]. Firstly, the column was injected with dilute HCl (5 wt%) and the both ends of the column were sealed by silica gel pads. ...
A serpentine-shaped semi-packed micro gas chromatography (GC) column with mesoporous inner surface and ionic liquid (IL) coating was developed for the separation of various typical volatile organic compounds in exhaled air. The mesoporous surface was prepared by coating silica nanoparticles on the inner surface of the micro GC column through static method and used as stationary phase support to improve the separation performance by its high surface area. The micro GC columns provide efficient separations for analytes including nonpolar (alkanes), weak polar (benzene series) and polar compounds (alcohols), as well as various typical markers of non-alcoholic fatty liver disease. The test results show that the resolution of most analytes is higher than 1.5, the elution peaks are symmetrical. Moreover, due to the chemical stability of IL, the micro GC had good repeatability, thermal stability and oxygen robustness. The maximum relative standard deviation of retention time was 0.44% in four weeks. During the programmed heating, a stable baseline was achieved and the baseline drift value was less than 4.8 mV when the operating temperature increased from 50 °C to 140 °C. The oxygen robustness was verified by a decrease of 7.2% in the peak capacity after exposure to dry air at 140 °C for 48 h. These characteristics showed the micro GC column is suitable for a portable breath analyzer.
... A typical preconcentrator made of silicon is illustrated in Fig. 2a. This material provides low thermal mass, uniform thermal distribution, and the ability to handle high temperature ramping rates [48], the most relevant features in miniaturized preconcentrators. ...
... On the contrary, dry etching techniques offers the possibility to create high aspect ratio structures. In this process, etching is conducted by ions that collide and react with the exposed surface of the silicon wafer instead of using liquid chemicals [48]. The most widespread technique for creating cavities, channels, and pillars with different geometries in silicon-based PC is the deep reactive ion etching (DRIE). ...
... Anodic bonding is the most common technique for silicon-glass bonding [6][7][8]19,34,36,37,[51][52][53]. In this process, a DC voltage ranging from 500 to 2000 V is applied between the substrates whereas they are heated to temperatures varying from 300 to 600 • C [48]. The generated electric field leads to the migration of Na + ions from the silicon/glass interface, leaving oxygen ions (O 2− ). ...
In the last years, a growing number of fields such as air quality monitoring, breath analysis or explosives and chemical warfare agents detection requiring fast, on-site, sensitive analysis has led to the development of portable gas chromatography systems. In most cases, these systems integrate a miniaturized gas preconcentrator, which provides a significant enhancement of the sensitivity enabling quantification of analytes present in the sample at trace levels. In this review, the authors have focused on recent developments in these preconcentrators integrated in portable gas chromatography systems. The main materials and fabrication techniques, designs, heating technologies, fluidic connections, adsorbents, and applications are discussed. In addition, an analysis of some factors affecting preconcentration performance is presented. A new figure of merit called Normalized Preconcentration Efficacy (NPE) is proposed to evaluate the performance of these devices in a standardized manner, making possible a more straightforward comparison between different devices.
... Silicon substrate was used in the fabrication of μGC (Figure 1), which is also the dominant platform for μGCs (22). Channel dimensions of μGC could be designed and tailored to optimize chromatographic performance. ...
... Channel dimensions of μGC could be designed and tailored to optimize chromatographic performance. Three major microchip column geometries have been reported: serpentine, circular spiral and square spiral (3,22). Circular spiral geometry was adopted for μGC column fabrication ( Figure 1). ...
... The circular spiral column has a coil-like pattern with no sharp turns. Serpentine column has sharp 180 • turns resulting in pooling of stationary phase in the curvatures, leading to chromatographic inefficiency (22). Such deleterious effects were all minimized in circular spiral columns. ...
Despite promising advances with metal-organic frameworks (MOFs) as stationary phases for chromatography, the application of MOFs for one- and two-dimensional micro-gas chromatography (μGC and μGC × μGC) applications has yet to be shown. We demonstrate for the first time, μGC columns coated with two different MOFs, HKUST-1 and ZIF-8, for the rapid separation of high volatility light alkane hydrocarbons (natural gas) and determined the partition coefficients for toxic industrial chemicals, using μGC and μGC × μGC systems. Complete separation of natural gas components, methane through pentane, was completed within 1 min, with sufficient resolution to discriminate n-butane from i-butane. Layer-by-layer controlled deposition cycles of the MOFs were accomplished to establish the optimal film thickness, which was validated using GC (sorption thermodynamics), quartz-crystal microbalance gravimetric analysis and scanning electron microscopy. Complete surface coverage was not observed until after ~17 deposition cycles. Propane retention factors with HKUST-1-coated μGC and a state-of-the-art polar, porous-layer open-tubular (PLOT) stationary phase were approximately the same at ~7.5. However, with polar methanol, retention factors with these two stationary phases were 748 and 59, respectively, yielding methanol-to-propane selectivity factors of ~100 and ~8, respectively, a 13-fold increase in polarity with HKUST-1. These studies advance the applications of MOFs as μGC stationary phase.
... In the last years, considerable efforts have been made in the area of micro-machined devices for fast 102 separation and detection, discussed recently by Ghosh et al. [9] with regard to column geometries, 103 coating procedures and interfaces to inlets and detectors. Still, most applications described on micro-GC 104 systems are restricted to volatile compounds, samples of limited complexity and rather small 105 concentration ranges [10]. ...
... The implementation of GC-MS is highly dependent on the costs of sample analysis, taking into account 278 instrument acquisition, consumption of energy and consumables, as well as waste management [45]. 279 Fast GC approaches such as resistive heating, have gained little popularity due to higher costs for special 280 manufactured columns, amongst others [4,8], whereas miniaturization of GC-MS has been realized at 281 the expense of analytical quality [9]. One of the biggest restrictions of miniaturized GC columns is the 282 limited loadability. ...
... Once this becomes economically lucrative, on-demand manufacturing of custom and complex designs, 361 such as µ-GC columns and interfaces, will attract increasingly attention to address limitations in areas 362 such as point-of-care and field applications [7,9,58,59]. Further progress on mobile GC-MS platforms is 363 expected with advances in transportation, such as autonomously operated robotic vehicles and analysis 364 drones, providing access to dangerous and inaccessible areas [50,60]. ...
Since the advent of gas chromatography - mass spectrometry (GC-MS), the evolution in high-performance GC-MS has boosted the quality and quantity of information. Continuing technical advances and topics of current focus are pushing GC-MS in areas such as metabolomics, biochemistry, medical analysis, and pharmacology, traditionally dominated by other separation techniques. Still, selection and optimization of sample preparation, analysis and data evaluation need to be carefully assessed to address the purpose of the analytical question, both in targeted and non-targeted approaches. In particular, studies on increasingly complex samples require sophisticated techniques. In this review, recent and significant advances in GC-MS are discussed, which includes a brief overview of challenges and limitations as well as solutions. Trends towards softer ionization techniques, high-resolution MS and multidimensionality further extend the analyte range in GC-MS. Especially, the implementation of standardized and streamlined workflows will enable the exploitation of the full potential of GC-MS in future.
... Due to its widespread employment in various areas [1][2][3][4], continuous advancements are being made to improve the speed and performance of GC methods [5,6]. One area that is emerging as an important development for GC and other analytical techniques is miniaturization [7], which can afford many benefits including increased analysis speed, reduction of resource consumption and instrument portability [8][9][10][11]. ...
... In this regard, microfluidics has been a very effective tool. Of note, since the first miniaturized microfluidic GC (µGC) device was reported [12], many developments have been made in this field [7,13]. One area of on-going interest in µGC is the adaptation of detection methods. ...
A novel miniaturized gas chromatography–flame photometric detection device built within a titanium platform (Ti µGC–FPD) is presented. The 7.5 cm × 15 cm monolithic Ti device contains both an OV-101 coated separation column (5 m × 100 µm i.d.) and a shielded cavity to house the hydrogen-rich detector flame. The FPD employs a micro counter-current flame (about 250 µm in diameter) that is stabilized by opposing relatively low flows of oxygen and hydrogen (7–10 mL/min O2 and 40 mL/min H2). Under optimal conditions, the minimum detectable limits are about 70 pg S/s for sulfur and 8 pg P/s for phosphorous. The natural (i.e., unfiltered) selectivity for these responses over carbon is near 104.3 for S/C and 10⁵ for P/C. Even greater selectivity over hydrocarbons can further still be obtained by employing conventional interference filters. Overall, good separations with stable and sensitive detector performance are obtained with the device, and its sturdy Ti structure supports robust operation. Results indicate that this Ti µGC–FPD device may be a useful alternative approach for incorporating selective FPD sensing in µGC analyses.
Graphical Abstract
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... На первом этапе изготавливаются алюминиевая и полимерная на основе АБС (акрилонитрил бутадиен стирол, далее -полимерная) матрицы, используемые в качестве шаблонов при создании первой части планарных МФК. Алюминиевая матрица изготавливается методом микрофрезерования, полимерная матрица с использованием аддитивных технологий путем 3D-печати, при этом полученные шаблоны имеют одну конфигурацию и одинаковые геометрические характеристики, представленные на рисунке 1. Высокой производительностью отличаются МФК со змеевидной конфигурацией каналов за счет небольшого числа поворотов [7]. ...
Exhaled air is a matrix with a complex molecular composition, including more than 3,500 components of various origins, the content of which can indicate the normal or pathological state of human health. One of the selective markers of diabetes formed in exhaled air is acetone. Its increased content (more than2.54 mg/m3) in exhaled air indicates excessive levels of glucose in the blood. To carry out a diagnostically reliable quantitative analysis of acetone in exhaled air, it is necessary to minimize random errors at all stages of sampling, concentration and calibration. The proposed MFC allow to carry out sample preparation and calibration under identical conditions, while combining the stages of sampling and concentration. The sample was concentrated using microfluidic systems based on Silagerm 8040 filled with a sorbent. Porapak-Q was chosen as the sorbent, which was pre-treated with ethyl alcohol vapour before filling into the channels. Sorption concentration in dynamic mode using an MFC was carried out by passing the resulting model gas mixture “acetone in air” with a concentration of 2.54 mg/m3 at t = 0oC until breakthrough appears. Desorption using the MFC based on Porapak-Q was carried out at temperatures of 50°C, 60°C, 70°C in dynamic mode by passing purified air at a rate of 0.5 ml/sec (desorption time is one second). The effluent was analysed by gas chromatography. The main advantage of this system is the ability to include it in a gas microchromatograph. The resulting analytical complex is mobile, which allows the usage for non-invasive diagnostics in non-laboratory conditions. Optimal concentration conditions using the MFC filled with Porapak-Q sorbent at which the maximum concentration coefficient of 43 was achieved have been established (tsorb=0oC; tdes=70oC, Vsorb=45 ml, tdes=1 sec). In a comparative analysis of the standard sampling method (using a Tedlar bag) and the method proposed using the MFC, it was found that the use of Tedlar bags for sampling exhaled air resulted in significant decrease in the accuracy characteristics (more than 30-65%) within 12 h, which is not applicable for diagnostic purposes. This fact was due to the sorption of the analyte on the walls of the bag and to eliminate undesirable effects it is necessary to use an additional step of sample drying. When the MFC was used for sampling, such a tendency was not observed, the accuracy characteristic did not decrease by more than 6-10% within 8 hours and no additional stages of drying the sample of exhaled air were required.
... Other researchers have also added major contributions [9,[11][12][13][14][15][16][17][18][19][20][21][22][23] in the development of μGC systems that have increased GC portability. Thorough review articles on μGC [24][25][26][27][28][29] provide much more exhaustive details not presented here. ...
This paper presents developments in stationary phase coatings for microelectromechanical system gas chromatography (MEMS GC). Specifically, we present the coating of MEMS GC separation columns with a chiral stationary phase for the separation of amino acid enantiomers. Three commercial columns coated with chiral stationary phases from Restek were tested: Rt-βDEXm, Rt-βDEXsm, and Rt-βDEXsa. Four amino acid enantiomers (d- and l-) were tested with the 3 commercial columns: alanine (Ala), valine (Val), leucine (Leu), and aspartic acid (Asp). The Rt-βDEXsm column provided the best experimental performance with separation of d- and l-Ala and partial separation of d- and l-Asp. The resolution, Rs, values were 4.65 for the Ala enantiomers and 0.98 for the Asp enantiomers, respectively. The Rt-βDEXsm chiral stationary phase was dynamically coated on three 10-m-long microcolumns connected in series to investigate amino acid enantiomer separation. Successful separation of d- and l-Ala and partial separation of d- and l-Asp were observed with the microcolumns. The Rs values from the chiral-stationary-phase-coated microcolumns were 1.21 and 0.553 for the Ala and Asp enantiomers, respectively. The chromatographically separated amino acid enantiomers were detected by the MAss Spectrometer for Planetary EXploration (MASPEX), a spaceflight mass spectrometer. Future work is required for improving the MEMS GC separation column performance consisting of testing static versus dynamic coating methods and more rigorous investigation of the stationary phase coating thickness. A discussion is provided on future work for the development of an MEMS GC suite targeting broad analyte selectivity for future space science missions.
... These processes allow for precise microscale features, but they are only compatible with a few materials and lack the ability to form complex 3D designs. Some microfluidic applications like micro heat exchangers or microcolumns for gas chromatography could benefit from the design flexibility inherent in additive manufacturing (Dahmen et al., 2020) but call for high temperatures and high thermal conductivity (Ghosh et al., 2018). Laser powder bed fusion (LPBF) is one method that has been used to form metal microchannels for microfluidic applications (Gupta et al., 2016;Phyo et al., 2020), but powder removal from channels with large aspect ratios is challenging (***REFS). ...
High-temperature microfluidic devices (such as gas chromatography microcolumns) have traditionally been fabricated using photolithography, etching, and wafer bonding which allow for precise microscale features but lack the ability to form complex 3D designs. Metal additive manufacturing could enable higher complexity microfluidic designs if reliable methods for fabrication are developed, but forming small negative features is challenging—especially in powder-based processes. In this paper, the formation of sealed metal microchannels was demonstrated using stainless-steel binder jetting with bronze infiltration. To create small negative features, bronze infiltrant must fill the porous part produced by binder jetting without filling the negative features. This was achieved through sacrificial powder infiltration (SPI), wherein sacrificial powder reservoirs (pore size ∼60 μm) are used to control infiltrant pressure. With this pressure control, the infiltrant selectively filled the small pores between particles in the printed part (pore size ∼3 μm) while leaving printed microchannels (700 μm, 930 μm) empty. To develop the SPI method, a pore-filling study was performed in this stainless-steel/bronze system with 370 μm, 650 μm, and 930 μm microchannel segments. This study enabled SPI process design on these length scales by determining variations in pore filling across a sample and preferential filling between different-sized pores.
... Hyphenated chromatography techniques have excellent separation ability and detection sensitivity, by analyzing a large number of samples in a very short time with accurate and reliable identification [2][3][4]. However, the conventional chromatography equipment is high in power consumption, bulky, slow in analysis time, and high-cost, and it is not suitable for real-time analysis and monitoring [5][6][7]. Micro GC (µGC) is a novel separation technique targeted at the analysis of volatile organic compounds (VOCs) with the development of micro electromechanical system [8]. The reduction of µGC system size and power consumption through the miniaturization of individual components enables real-time, rapid, and on-site analysis of complex gas mixtures. ...
In this paper, the μGC-IL/MOF and the μGC-IL were prepared using [P66614][NTf2]/ZIF-8 and [P66614][NTf2] as the stationary phase, respectively. [P66614][NTf2]/ZIF-8 composite stationary phase material has high specific surface area and porous structure, which increases the diffusion of gas molecules in the column. Compared to μGC-IL, μGC-IL/MOF can separate n-alkanes mixture (C5–C12) and lung cancer biomarkers (pentane, isoprene, acetone, benzene, 2-pentanone) with higher resolution, and the resolution (R) of pentane and isoprene was increased by 257.00% in particular. The μGC-IL/MOF can separate lung cancer biomarkers in about 5 min with optimal carrier gas velocity and column temperature. The retention times of pentane, isoprene, acetone, benzene, and 2-pentanone were 0.884 min, 1.246 min, 1.634 min, 2.204 min, and 3.049 min, respectively. The resolutions of adjacent peaks were 1.785, 1.525, 2.521, and 3.514, respectively. Which meets the requirements of quantitative analysis (R > 1.5). Therefore, the μGC-IL/MOF is expected to be integrated into portable devices for environmental monitoring and medical diagnosis in the future.
... A decades-old technique like a miniaturized or micro gas chromatograph (μGC) is now connected to a mass spectrometer (MS) that shows higher sensitivity and selectivity for the analysis of gases and VOCs. [233][234][235][236][237] μGC-MS technique involves several repetitive modules of μ-GC and a quadrupole mass spectrometer for identifying target gases. Each module consists of a micro-injector or pre-concentrator for sample introduction, a micromachined chromatographic column for gas separation, and a non-destructive thermal conductivity microdetector (μ-TCD) or array of detectors. ...
Selectivity is one of the most crucial figures of merit in trace gas sensing, and thus a comprehensive assessment is necessary to have a clear picture of sensitivity, selectivity, and their interrelations in terms of quantitative and qualitative views. Recent reviews on gas sensors/techniques are limited to specific sensors, sensors with unconventional materials, various technological exploitation, or specific applications. However, the selectivity is either unexplored in most cases or explained concerning the materials/techniques involved in a demonstration. Therefore, there is a pressing need to identify the possible ways to improve the selectivity of a gas sensor/technique with low or zero cross-sensitivity to other compounds/gases present in the working environment. Analytical techniques involving spectroscopic and mass-spectrometry-based methods are excellent in selectivity but have limited applicability for field deployment compared to the miniatured solid state sensors. Solid state sensors are the mainly studied gas sensors due to their flexibility, portability, and cost-effectiveness, and being technologically favorable but suffer from low selectivity in harsh and humid environments. This review will evaluate the limitations and possible solutions to selectivity issues in a wide variety of gas sensors. Here, we have discussed the gas-sensor technologies and underlying sensing mechanisms in two main groups - spectroscopic and non-spectroscopic. Recent state-of-the-art techniques and fundamental challenges are discussed to improve the selectivity and other gas sensor indicators and future perspectives.
... However, in the EO field, most studies in the literature concerning μGC based on MEMS are focused on MEMS-based columns[90][91][92][93], probably because the separation step is manda-tory during their GC analysis. In this respect, in 2016, Cagliero et al.[94] developed highly efficient MEMSbased columns (N/m above 8000) for the analysis of the plant volatiles, in particular for EOs. ...
This review is an overview of the recent advances of gas chromatography in essential oil analysis; in particular, it focuses on both the new stationary phases and the advanced analytical methods and instrumentations. A paragraph is dedicated to ionic liquids as GC stationary phases, showing that, thanks to their peculiar selectivity, they can offer a complementary contribution to conventional stationary phases for the analysis of complex essential oils and the separation of critical pairs of components. Strategies to speed‐up the analysis time, thus answering to the ever increasing request for routine essential oils quality control, are also discussed. Last but not least, a paragraph is dedicated to recent developments in column miniaturization in particular that based on microelectromechanical‐system technology in a perspective of developing micro‐gas chromatographic systems to optimize the energy consumption as well as the instrumentation dimensions. A number of applications in the essential oil field is also included. This article is protected by copyright. All rights reserved
... The microfluidic technologies of liquid and gas have been studied for a long time, and microfluidic LC and GC were established based on the lab-on-a-chip technology. 49,50) In addition to these types of chromatography, a lab-on-a-chip for SFC has been recently reported. 51) The SFC flow way was made on a glass chip. ...
Supercritical fluid chromatography (SFC) has unique separative characteristics distinguished from those of HPLC and gas chromatography. At present, SFC is widely used and there are many applications in various biological, medical, and pharmaceutical fields. In this review, we focus on recently developed novel techniques related to SFC separation including: new column stationary phases, microfluidics, two-dimensional separation, and gas–liquid separation. In addition, we discuss the application of SFC using a water-containing modifier to biological molecules such as amino acids, peptides, and small proteins that had been challenging analytes.
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... Micro-gas chromatography (µGC) systems have shown immense growth in the last two decades [1][2][3][4][5]. It provides a less invasive option for gas analysis that can be monitored in real time and offer reliable quantitative data in essential sectors, including industry, healthcare, environment, and national security. ...
The miniaturization of gas chromatography (GC) systems has made it possible to utilize the analytical technique in various on-site applications to rapidly analyze complex gas samples. Various types of miniaturized sensors have been developed for micro-gas chromatography (µGC). However, the integration of an appropriate detector in µGC systems still faces a significant challenge. We present a solution to the problem through integration of µGC with photonic crystal slab (PCS) sensors using transfer printing technology. This integration offers an opportunity to utilize the advantages of optical sensors, such as high sensitivity and rapid response time, and at the same time, compensate for the lack of detection specificity from which label-free optical sensors suffer. We transfer printed a 2D defect free PCS on a borofloat glass, bonded it to a silicon microfluidic gas cell or directly to a microfabricated GC column, and then coated it with a gas responsive polymer. Realtime spectral shift in Fano resonance of the PCS sensor was used to quantitatively detect analytes over a mass range of three orders. The integrated µGC–PCS system was used to demonstrate separation and detection of a complex mixture of 10 chemicals. Fast separation and detection (4 min) and a low detection limit (ng) was demonstrated.
... Nonetheless, compared to conventional capillary columns, µ-columns are several magnitudes shorter, noncylindrical, and normally microfabricated on top of planar substrates, using a chip-based configuration [228]. The separation performance of µ-columns will depend on the optimization of several factors, such as: (i) channel cross-section (e.g., rectangular, square, trapezoidal, or semicircular), (ii) channel design (e.g., circular or square spiral, serpentine, zigzag, radiator, or wavy), (iii) column typology (e.g., open, semipacked, or monolithic columns), (iv) substrate material, (v) stationary phase, (vi) operating temperatures, (vii) flow rate, and (viii) carrier gas [229]. Metal, glass polymers, and silicon-based materials are the most common substrates used in µ-columns, due to their good physical, thermal, and chemical properties [230]. ...
In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans' olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoring.
... Whereas ILs are well proven for capillary columns, their use in microcolumns started recently by Zellers and Agah groups [4,27]. Extensive and up-to-date reviews on microcolumns, stationary phases, and separation performances have been recently published [9,28]. Despite the emergence of organic monolithic columns for conventional gas chromatography (GC) application in the 1970s, as an alternative to packed columns, their use quickly faded due to higher performances shown by open tubular columns [29,30]. ...
... Ainsi, la GC × GC permet également d'améliorer les limites de détections par rapport à la GC 1D. Le milieu pétrolier a largement tiré profit des différents avantages de la GC × GC [266]. ...
L’air expiré présente un intérêt pour des applications médicales comme le dépistage, le suivi de pathologies ou d’expositions. En effet, cet échantillon contient des marqueurs volatils endogènes ou exogènes et son prélèvement est non invasif. Même si le prélèvement est simple, la complexité et la variabilité de l’air expiré expliquent le peu de tests autorisés par les autorités sanitaires.Cette thèse s’est intéressée à deux outils analytiques pour l’analyse de l’air expiré : une puce de préconcentration et la chromatographie en phase gazeuse intégralement bidimensionnelle. Ces deux techniques, peu explorées jusqu’à présents dans ce domaine, peuvent présenter un intérêt en simplifiant le prélèvement et en permettant une analyse plus exhaustive des marqueursLe travail effectué sur la puce de préconcentration a montré que les micropréconcentrateurs fabriqués au laboratoire prélèvent et injectent des mélanges de gaz modèles et des échantillons d’air expiré avec des variabilités proches des systèmes de laboratoires. De plus, nos travaux ont montré que ces micropréconcentrateurs présentent deux avantages majeurs en réduisant les volumes d’échantillon nécessaires et en s’intégrant dans des systèmes simples, portables et fonctionnant sur batterie. Afin d’illustrer leur intérêt sur un cas réel simple, nous avons utilisé ces micropréconcentrateurs pour étudier trois marqueurs du tabagisme dans l’air expiré de trois fumeurs et de trois non-fumeurs et suivre les cinétiques de ces composés dans l’air expiré d’une personne. Finalement, nous avons effectué un travail préliminaire d’intégration dans des échantillonneurs dédiés afin d’exploiter les avantages des micropréconcentrateurs pour le prélèvement de l’air expiré et tenter d’obtenir un prélèvement sur une expiration unique.Nous avons ensuite choisi et reproduit une architecture de modulateur fluidique simple, pertinente pour la miniaturisation, basée sur un Dean’s switch. Nous avons montré que ce modulateur décrit en 2016 était compatible avec une injection par thermodésorption et comparé ses performances à la GC simple pour l’analyse d’un même échantillon d’air expiré. Ceci a montré que cette architecture présente un intérêt en modulant des composés exhalés très volatils ce qui permet de nombreuses levées de coélution. Finalement, nous avons montré, grâce à des plans d’expériences, que l’amélioration des performances de ce modulateur nécessitait un contrôle minutieux des paramètres.Enfin, nous avons confronté nos outils à des échantillons d’une malade atteinte d’une maladie rare, la phénylcétonurie. Des échantillons d’espace de tête d’urine et d’air expiré de la patiente ont été prélevés. Les résultats, incomplets à ce stade, sont discutés dans le manuscrit.
... They can have different type of cross section, like as square, semi-circular, trapezoidal or rectangular. [129] Generally, a few types of materials can be used for preparation of GC column for microchip gas chromatography. The most widely used material is silicon and also some research groups use glass. ...
A chromatographic column is the fundamental element required for gas-chromatographic analysis. The separation of components coming from complex mixtures, prior to their detection was leading to a prominent revolution in different areas of science. Moreover, current advances in gas chromatographic (GC) columns technology and development have been providing almost unlimited possibilities for analysis employing diverse matrices. We aim through this review article to describe the evolution of chromatographic columns, by pointing the most important stages, as well as the new trends and future perspectives predicted for the new generation of GC columns. Furthermore, it was in our scope to present the main fundamentals regarding the theoretical relationships that describe the chromatographic separation, to introduce concepts related to columns selection in accordance with the required application as well as to discuss the available evaluation parameters for columns efficiency. Consequently, the early stages of first columns preparation up to the development of GC capillary columns used nowadays, together with examples of their applications are also reported and described in detail.
... Recently, Azzouz et al. [13] briefly reviewed microelectromechanical systems (MEMS)-based gas chromatography systems. Ghosh et al. [14] reviewed the developments in microchip GC column technology and in interfacing GC microchips to injectors and detectors. In this review, some general aspects of detectors will be introduced first, and then the miniaturization of conventional detectors and the development of new detectors for μGC will be investigated. ...
Micro gas chromatography (μGC) has been continuously gaining attention since the last century owing to multiple favorable characteristics, such as its small size, low power consumption and minimal production and maintenance costs. μGC has the potential to provide practical solutions to emerging analytical challenges in security, health, and environment. In this review, we summarize recent advances in micro detectors for μGC, including the study of the miniaturization of conventional detectors and the development of novel detectors for μGC chromatography.
An important field of research is the miniaturization of analytical systems for laboratory applications and on-field analysis. In particular, gas chromatography (GC) has benefited from the recent advances in enabling technologies like photolithography, micromachining, hot embossing, and 3D-printing to improve sampling and sample preparation, microcolumn technologies, and detection. In this article, the developments and applications reported since 2015 were reviewed and summarized. Important applications using benchtop instruments, portable GCs, and micro-GCs (µGCs) were showcased to illustrate the current challenges associated with each miniaturized interfaces and systems. For instance, portable instruments need to be energy-efficient and ideally depend on renewable sources for carrier gas generation. Lastly, multidimensional separations were addressed using miniaturized systems to effectively improve the peak capacity of portable systems.
The present study investigated the use of a dedicated gas chromatography (GC) column (L = 70 cm, 75 μm deep, and 6.195 mm wide) with radially elongated pillars (REPs) as the second column in a comprehensive two-dimensional gas chromatography (GC × μGC) system. Three stationary phases [apolar polydimethylsiloxane (PDMS), medium polar room-temperature ionic liquid (RTIL) based on monocationic phosphonium, and polar polyethylene glycol (PEG-1000)] have been coated using the static method at constant pressure or using an original vacuum pressure program (VPP) from 400 to 4 mbar. The best efficiency reached up to N = 62,000 theoretical plates for a film thickness of 47 nm at 100 °C for an iso-octane peak (k = 0.16) at an optimal flow rate of 4.8 mL/min. The use of the VPP improved the efficiency by approximately 15%. Efficiencies up to 28,000 and 47,000 were obtained for PEG-1000 and RTIL, respectively. A temperature-programmed separation of a mixture of 11 volatile compounds on a PDMS-coated chip was obtained in less than 36 s. The PDMS-, PEG-1000-, and RTIL-coated chips were tested as the second column using a microfluidic reverse fill/flush flow modulator in a GC × μGC system. The REP columns were highly compatible with the operating conditions in terms of flow rate and with more than 30,000 plates for the iso-octane peak. Moreover, a commercial solvent called white spirit containing alkanes and aromatic compounds was injected in three sets of columns in normal and reverse modes, demonstrating the great potential of the chip as a second-dimension separation column.
Natural product analyses must cover a wide range of topics, and they commonly have to deal with very complex samples. The development of appropriate sample preparation and analytical methods is therefore fundamental to obtain the required level of information.
Conventional extraction and separation methods entail the use of a considerable amount of sample and reagents and high energy consumption. However, greener alternative can be adopted.
The present chapter presents the sample preparation and analytical solutions that can be adopted to make the analysis of natural products more sustainable. Particular attention will be focused on the strategies for in situ and in vivo analysis through miniaturized and portable devices and instrumentations.
Gas chromatography is the most mature of all chromatographic techniques. It can be performed with a solid or liquid stationary phase although most separations are performed with the latter. Materials used as stationary phases for both techniques are described. Mobile phases for GC are not interactive but they still play an important role in the separation process. Mobile phase selection and instrumental settings are discussed. Detection of eluted compounds is an essential part of the process and details are provided for the most common detectors. Although GC is a mature technique there are still innovative approaches that are described. The chapter concludes with a brief description of the separation mechanism in GSC and GLC plus broad aspects of applications.
Micro pillar array column with interpillar distance of 2.5 µm for pillars diameter of 5 µm has been introduced in high pressure gas chromatographic systems for online industrial analysis. Separation of gas mixtures have been performed under carrier gas pressure as high as 60 bar using rotating valve for gas injection without sample decompression stage prior to injection. A very low intrinsic height equivalent to a theoretical plate value of 14 µm has been obtained in few seconds. Instead of conventional gas chromatography, carrier gas nature such as helium, argon and carbon dioxide and pressure can be used to tune the selectivity. Liquid hydrocarbon samples have been successfully introduced in the column using a septum based split/splitless injector modified to work up to 40 bar. Separations of VOCs and gasoline samples have been successfully performed.
Conventional high-performance liquid chromatography (HPLC) and gas chromatography (GC) are the most widely used analytical tools in the analytical chemistry field. However, these successful techniques present a number of unfriendly environmetal issues. Thus, conventional HPLC needs large amounts of organic solvents and generates high amounts of wastes, conventional GC mostly uses non-renovable and expensive gases such as He (particularly when combined with mass spectrometry), and conventional HPLC and GC are both time- and high energy-demanding. This review describes recent modifications (2018-2020) introduced in HPLC and GC techniques to improve their greeness, covering topics such as mobile phases and mobile phase additives, novel stationary phases, and mostly the minituarization of the equipments with the purpose of simplification and costs reduction.
This paper utilizes a combined approach of the convection‐diffusion theory and the moment analysis to conduct a comprehensive investigation of the solute dispersion under the influence of the interphase transport in finitely long inner coated microchannels. The present work has threefold novel contributions: (1) The 2D solute concentration contours in the stationary phase are calculated for the first time to facilitate the understanding the role of the interphase transport in the solute dispersion in the mobile phase. (2) The skewness of the elution curves is investigated to guide the control of solute band shape at the channel outlet. (3) The 2D diffusion‐convection theory and zero‐dimensional (0D) moment analysis complement each other to present a characterization of the solute dispersion behaviors more comprehensive than that by either of the two methods alone. Parametric studies are performed to clarify the effects of four major parameters related to the interphase transport (i.e., stationary phase Péclet number, interphase transport rate, partition coefficient, and stationary phase thickness) on the solute dispersion characteristics. The results from this study provide a straightforward understanding of the effects of interphase transport on the solute dispersion in finitely long microchannels and are of potential relevance to the design and operation of the microfluidics‐based analytical devices.
Isomers, holding similar chemical and physical properties, are difficult to separate especially by utilizing a microfabricated gas chromatography system due to limited column lengths mainly imposed by low-pressure (<20 kPa) micropump capability. In this paper, we demonstrated the separation of a pair of structural isomers, isopentane and pentane, in a micro-scale gas chromatography system with a circulatory loop of two 25-cm micro open tubular columns, while operating under a minimal pressure requirement of <10 kPa. The developed micro circulatory gas chromatography (MCGC) system achieved an effective column length of 12.5 meters by circulating the isomer gases for 25 cycles, the longest micro open tubular column length ever reported by any microfabricated GC systems yet.
The determination of the identity and quantity of hydrocarbon composition in water and soil matrices is critical in several applications. This chapter discusses the analytical approaches of both class‐type separations, as well as detailed hydrocarbon determinations as applied to cases where addressing potential environmental impact is the concern. Total petroleum hydrocarbons are a measure of all extractable hydrocarbons in a sample by a given analytical method. It is often used to identify and monitor environmental samples for oil and gas contamination. Soil composition, like that of petroleum products, varies greatly in physical and chemical properties. Soil mineral particles are divided into three classes, based on size and chemical properties: sand, silt, and clay. The chapter presents a broad overview of gravimetric, immunoassay, infrared spectroscopy, and gas chromatography methods. In environmental forensic investigations, a chemical fingerprint, or the unique pattern of a source, can be utilized to support expert opinions regarding sources of environmental contamination.
In this work, 3D-printed metal column was developed towards micro gas chromatography (GC) applications and its properties and gas separation performances were characterized. By using Ti6Al4V Grade 23 powder, a square spiral one-meter-long column (3D-column) was 3D-printed in a planar substrate of 3.4 × 3.3 × 0.2 cm and then perhydropolysilazane was deposited as a pretreatment agent, followed by coating stationary phase (OV-1) onto the inner wall of the micro-channel. The circular channel and ports of 3D-column were confirmed as uniform by 3D X-ray microscopy without any distortion. The physical and thermal properties of the 3D-column were found to be very similar to that of standard Ti6Al4V Grade 23 alloy with near zero porosity. The 3D-column with pretreatment and stationary coating demonstrated more superb separation performance of gas mixtures and lower column bleed effect than bare or pretreated-only 3D-column in terms of peak shape, broadening, and resolution. In addition, the thermal responses and stability of the 3D-column promise its applicability as high temperature GC applications.
The paper presents a parallel micro gas chromatography approach using three ionic liquid semi-packed columns. Switching from a single column to multiple parallel columns with different selectivity enhances the power of compound identification without increasing the analysis time. The columns are fabricated using microelectromechanical systems (MEMS) technology containing an array of microfabricated pillars. The columns are 1 m-long and 240 μm-deep with four pillars per row. All columns were functionalized with ionic liquid stationary phases using a modified static coating technique and demonstrated the number of theoretical plates between 5000 to 8300 per meter. The chip performance was investigated with four different samples: 1) a mixture of C7-C30 saturated alkanes, 2) a multi-analyte mixture consisting of twenty compounds ranging from 80 °C to 238 °C in boiling point, 3) a mixture of five organic chemicals with varying degrees of polarity, and 4) 46-compound mixture containing all the chemicals in the first three samples. The individual columns separated 75%-100% of the first three samples but failed to distinguish all 46 compounds due to co-eluting analytes; however, the parallel configuration provided more retention time information by which all the compounds in all samples were fully determined.
Since the late 1970s, approaches have been proposed to replace conventional gas chromatography apparatus with silicon-based microfabricated separation systems. Performances are expected to be much improved with miniaturization owing to the reduction of diffusion distances and better thermal management. When it is easy to microfabricate miniaturized parts, the main challenge consists, however, to produce stable, efficient, and functionalized columns. The purpose of the paper is to transpose and adapt monolith synthesis in-situ micromachined gas chromatography columns. Silica-based monolithic microcolumns based on the sol–gel process were tested in the course of high-speed gas chromatographic separations of light hydrocarbons mixture (C1–C4). At the optimum separation conditions, a very good resolution (2.14) for very light compounds (C1–C2) was reached on a 50 cm microcolumn at room temperature with a back-pressure within the range used at gas chromatography facilities (without external modification of the device). The versatility of these microelectromechanical systems (MEMS) columns was demonstrated with a high-temperature C1–C2 separation, and unsaturated cyclic alkanes. Light halogenated alkanes were also successfully separated. These columns should be used in various applications related to oil/gas and environment field analyses.
In this paper we report the first integration of a silicon microfabricated gas chromatography column with an ion trap mass spectrometer. The MEMS-column is fabricated in all silicon materials, with an integrated platinum resistive heater and temperature sensors. This design enables low power operation and rapid temperature heating, which are both useful for temperature programmed separations. The ion trap mass spectrometer has miniaturized electronics, including a compact RF generator, miniature detector system and control electronics which form the walls of the vacuum chamber. The integrated system has been demonstrated to separate a model mixture containing chemicals from different functional groups in under 22 min, while only consuming less than 15 W of power (30 W with vacuum pump).
A gas chromatographic approach for the determination and quantification of trace levels of carbon oxides in gas phase matrices for in situ or near‐line/at‐line analysis has been successfully developed. Catalytic conversion of the target compounds to methane via the methanation process was conducted inside a metal 3D‐printed jet that also acted as a hydrogen burner for the flame ionization detector. Modifications made to a field transportable gas chromatograph enabled the leveraging of advantaged microfluidic‐enhanced chromatography capability for improved chromatographic performance and serviceability. The compatibility with adsorption chromatography technology was demonstrated with in‐house constructed columns. Sustained reliable conversion efficiencies of greater than 99% with respectable peak symmetries were attained at 400°C. Quantification of carbon monoxide and carbon dioxide at a parts‐per‐million level over a range from 0.2 ppm to 5% (v/v) for both compounds with a respectable precision of less than 3% RSD for peak area (n = 10) and a detection limit of 0.1 ppm (v/v) was achieved. Linearity with correlation coefficients of R2 greater than 0.9995 and measured recoveries of > 99% for spike tests were achieved. The 3D‐printed steel jet was found to be reliable and resilient against potential contamination from the matrices owing to the in situ backflushing capability. This article is protected by copyright. All rights reserved
A small, consumable-free, low-power, ultra-high-speed comprehensive GCxGC system consisting of microfabricated columns, NanoElectroMechanical System (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble holdup time is demonstrated with a downstream FID. The analysis time of the second dimension was 160 ms, and peak widths in the second dimension range from 10-60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20,000 runs of the GCxGC columns with the NEMS resonators using a 4-component test set is presented. The GCxGC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector.
Miniaturization of gas chromatography (GC) instrumentation is of interest because it addresses current and future issues relating to compactness, portability and field application. While incremental advancements continue to be reported in GC with columns fabricated in microchips (referred to in this paper as " microchip columns "), the current performance is far from acceptable. This lower performance compared to conventional GC is due to factors such as pooling of the stationary phase in corners of non-cylindrical channels, adsorption of sensitive compounds on incompletely deactivated surfaces, shorter column lengths and less than optimum interfacing to injector and detector. In this work, a GC system utilizing microchip columns was developed that solves the latter challenge, i.e., microchip interfacing to injector and detector. A microchip compression clamp was constructed to heat the microchip (i.e., primary heater), and seal the injector and detector fused silica interface tubing to the inlet and outlet ports of the microchip channels with minimum extra-column dead volume. This clamp allowed occasional operation up to 375 • C and routine operation up to 300 • C. The compression clamp was constructed of a low expansion alloy, Kovar TM , to minimize leaking due to thermal expansion mismatch at the interface during repeated thermal cycling, and it was tested over several months for more than one hundred injections without forming leaks. A 5.9 m long microcolumn with rectangular cross section of 158 m × 80 m, which approximately matches a 100 m i.d. cylindrical fused silica column, was fabricated in a silicon wafer using deep reactive ion etching (DRIE) and high temperature fusion bonding; finally, the channel was coated statically with a 1% vinyl, 5% phenyl, 94% methylpolysiloxane stationary phase. High temperature separations of C10-C40 n-alkanes and a commercial diesel sample were demonstrated using the system under both temperature programmed GC (TPGC) and thermal gradient GC (TGGC) conditions. TGGC analysis of a complex essential oil sample was also demonstrated. Addition of a secondary heater and polyimide insulation proved to be helpful in achieving the desired elution temperature without having to raise the primary heater temperature above 300 • C for high boiling point compounds.
A titanium miniature gas chromatography device with an on-board micro-flame ionization detector (Ti µGC-FID) is presented. The design is based on a counter-current method that establishes a stable flame (~240 µm diameter) inside a 1.44 mm circular cavity within the Ti tile. The width of this cavity is found to have a significant impact on flame stability and detector performance. Through polarizing the conductive Ti tile body and situating a collector adjacent to the cavity, useful µFID response is obtained from the flame. The 7.5 cm × 15 cm rectangular monolithic Ti device contains a serpentine column layout (5 m long × 100 μm wide) coated with OV-101 stationary phase that is directly integrated with the on-board μFID. The column produces reasonable analyte peak symmetry and separation performance with a plate height of 1.5 mm for dodecane. Under optimized conditions, the Ti μGC-FID device yields a detection limit of 9 × 10⁻¹² gC s⁻¹, a linear response over 3 orders of magnitude, a sensitivity of 60 mC gC⁻¹, and a signal reproducibility within 5% RSD (n = 10). Some samples are analyzed using the Ti µGC-FID device and results indicate that this approach can potentially provide a useful alternative means of achieving sensitive and stable μFID performance within a robust, integrated miniaturized GC platform.
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In this study, a simple process for fabricating a novel micromachined preconcentrator (μPCT) and a gas chromatographic separation column (μSC) for use in a micro gas chromatograph (μGC) using one photomask is described. By electroless gold plating, a high-surface-area gold layer was deposited on the surface of channels inside the μPCT and μSC. For this process, (3-aminopropyl) trimethoxysilane (APTMS) was used as a promoter for attaching gold nanoparticles on a silicon substrate to create a seed layer. For this purpose, a gold sodium sulfite solution was used as reagent for depositing gold to form heating structures. The microchannels of the μPCT and μSC were coated with the adsorbent and stationary phase, Tenax-TA and polydimethylsiloxane (DB-1), respectively. μPCTs were heated at temperatures greater than 280 °C under an applied electrical power of 24 W and a heating rate of 75 °C s⁻¹. Repeatable thermal heating responses for μPCTs were achieved; good linearity (R² > 0.9997) was attained at three heating rates for the temperature programme for the μSC (0.2, 0.5 and 1 °C s⁻¹). The volatile organic compounds (VOCs) toluene and m-xylene were concentrated over the μPCT by rapid thermal desorption (peak width of half height (PWHH) <1.5 s); preconcentration factors for both VOCs are >7900. The VOCs acetone, benzene, toluene, m-xylene and 1,3,5-trimethylbenzene were also separated on the μSC as evidenced by their different retention times (47–184 s).
Monitoring Volatile organic compounds (VOCs) was a very important measure for preventing environmental pollution, therefore, a mini gas chromatography (GC) flame ionization detector (FID) system integrated with a mini H2 generator and a micro GC column was developed for environmental VOC monitoring. In addition, the mini H2 generator was able to make the system explode from far away due to the abandoned use of a high pressure H2 source. The experimental result indicates that the fabricated mini GC FID system demonstrated high repeatability and very good linear response, and was able to rapidly monitor complicated environmental VOC samples.
This paper reports a complete micro gas chromatography (μGC) system in which all the components are lithographically microfabricated and electronically interfaced. The components include a bi-directional Knudsen pump, a preconcentrator, separation columns and a pair of capacitive gas detectors; together, these form the iGC3.c2 system. All the fluidic components of the system are fabricated by a common three-mask lithographic process. The Knudsen pump is a thermomolecular pump that provides air flow to the μGC without any moving parts. The film heaters embedded in the separation columns permit temperature programming. The capacitive detectors provide complementary response patterns, enhancing vapor recognition and resolving co-eluting peaks. With the components assembled on printed circuit boards, the system has a footprint of 8×10 cm2. Using room air as the carrier gas, the system is used to experimentally demonstrate the analysis of 19 chemicals with concentration levels on the order of parts per million (p.p.m.) and parts per billion (p.p.b.). The tested chemicals include alkanes, aromatic hydrocarbons, aldehydes, halogenated hydrocarbons and terpenes. This set of chemicals represents a variety of common indoor air pollutants, among which benzene, toluene and xylenes (BTX) are of particular interest.
Miniaturized gas chromatography (µGC) systems hold potential for the rapid analysis of volatile organic compounds (VOCs) in an extremely compact and low-power enabled platform. Here, we utilize microfabrication technology to demonstrate the single chip integration of the key components of a µGC system in a two-step planar fabrication process. The 1.5 × 3 cm microfluidic platform includes a sample injection unit, a micromachined semi-packed separation column (µSC) and a micro-helium discharge photoionization detector (µDPID). The sample injection unit consists of a T-shaped channel operated with an equally simple setup involving a single three-way fluidic valve, a micropump for sample loading and a carrier gas supply for subsequent analysis of the VOCs. The innovative sample injection technique described herein requires a loading time of only a few seconds and produces sharp and repeatable sample pulses (full width at half maximum of approximately 200 ms) at a carrier gas flow rate that is compatible with efficient chromatographic separation. Furthermore, our comprehensive characterization of the chip reveals that a wide variety of VOCs with boiling points in the range of 110–216 °C can be analyzed in less than 1 min by optimizing the flow and temperature programming conditions. Moreover, the analysis of four VOCs at the concentration level of one part per million in an aqueous sample (which corresponds to a headspace concentration in the lower parts-per-billion regime) was performed with a sampling time of only 6 s. The µDPID has demonstrated a linear dynamic range over three orders of magnitude. The system presented here could potentially be used to monitor hazardous VOCs in real time in industrial workplaces and residential settings.
This work highlights a new bonding technique for micro-fabrication of an all silicon 3 meter gas chromatography column that could withstand the temperature cycling required for axial temperature programming. Proper separation of a complex gas mixture using a miniaturized GC column is critical in improving the overall performance of a lab on a chip system for environmental monitoring, medical diagnoses, and gas impurity measurement. To improve upon current methodology the column was first fabricated using micro-fabrication processes; experimentally validated using a high performance 3 meter GC column coated with OV-1 stationary phase. This process demonstrates that the bonding quality of the GC column to a 200 μm thick silicon lid was improved when using a new gold eutectic bonding technique. Furthermore, a new quality control technique was developed in order to test the overall bonding quality of the bonded pieces by fixing the bottom column and applying a mechanical shear force to the top lid. This m
In this work we present a high performance micro gas chromatograph column with a novel two dimensional axial heating technique for faster and more precise temperature programming, resulting in an improved separation performance. Three different axial resistive heater designs were simulated theoretically on a 3.0 m × 300 μm × 50 μm column for the highest temperature gradient on a 22 by 22 μm column. The best design was then micro-fabricated and evaluated experimentally. The simulation results showed that simultaneous temperature gradients in time and distance along the column are possible by geometric optimization of the heater when using forced convection. The gradients along the column continuously refocused eluting bands, offsetting part of the chromatographic band spreading. The utility of this method was further investigated for a test mixture of three hydrocarbons (hexane, octane, and decane).
A ready-to-deploy implementation of a microfabricated gas chromatography (μGC) system characterized for detecting hazardous air pollutants (HAPs) at parts-per-billion (ppb) concentrations in complex mixtures has been described. A microfabricated preconcentrator (μPC), MEMS separation column with on-chip thermal conductivity detector (μSC-TCD), flow controller unit, and all necessary flow and thermal management as well as user interface circuitry are integrated to realize a fully functional μGC system. The work reports extensive characterization of μPC and μSC-TCD for target analytes: benzene, toluene, tetrachloroethylene, chlorobenzene, ethylbenzene, and p-xylene. A Limit of Detection (LOD) of ∼1 ng was achieved, which corresponds to a sampling time of 10 min at a flow rate of 1 mL/min for an analyte present at ∼25 ppbv. An innovative method using flow-manipulation generated sharp injection plugs from the μPC even in the presence of a flow-sensitive detector like a μTCD. The μGC system is compared against conventional automated thermal desorption–gas chromatography–flame ionization detector (ATD–GC–FID) system for real gasoline samples in simulated car refueling scenario. The μGC system detected five peaks, including three of the target analytes and required ∼3 orders of magnitude lower sample volume as compared to the conventional system.
This paper reports a unique GC-on-chip module comprising a monolithically integrated semi-packed micro separation column (μSC) and a highly sensitive micro helium discharge photoionization detector (μDPID). While semi-packed μSC with atomic layer deposited (ALD) alumina as a stationary phase provides high separation performance, the μDPID implemented for the first time in a silicon-glass architecture inherits the desirable features of being universal, non-destructive, low power consumption (1.4 mW), and responsive. The integrated chip is 1.5 cm × 3 cm in size and requires a two-mask fabrication process. Monolithic integration alleviates the need for transfer lines between the column and the detector which improves the performance of the individual components with overall reduced fabrication and implementation costs. The chip is capable of operating under the isothermal as well as temperature and flow programming conditions to achieve rapid chromatographic analysis. The chip performance was investigated with two samples: 1) a multi-analyte gas mixture consisting of eight compounds ranging from 98 °C to 174 °C in boiling point and 2) a mixture containing higher alkanes (C9-C12). Our experiments indicate that the chip is capable of providing rapid chromatographic separation and detection of these compounds (<1 min) through the optimization of flow and temperature programming conditions. The GC-on-chip demonstrated a minimum detection limit of ~10 pg which is on a par with the widely used destructive flame ionization detector (FID).
The Microtechnology Center of Lawrence Livermore National Laboratory has developed a high performance hand-held, real time detection gas chromatograph (HHGC) by Micro-Electro-Mechanical-System (MEMS) technology. The total weight of this hand-held gas chromatograph is about 5 lbs., with a physical size of 8″ × 5″ × 3″ including carrier gas and battery. It consumes about 12 watts of electrical power with a response time on the order of one to two minutes. This HHGC has an average effective theoretical plate of about 40k. Presently, its thermal sensitive detector at PPM limits its sensitivity.
Like a conventional G.C., this HHGC consists mainly of three major components: 1) the sample injector, 2) the column, and 3) the detector with related electronics. The present HHGC injector is a modified version of the conventional injector. Its separation column is fabricated completely on silicon wafers by means of MEMS technology. This separation column has a circular cross section with a diameter of 100 μm. The detector developed for this hand-held G.C. is a thermal conductivity detector fabricated on a silicon nitride window by MEMS technology. A normal Wheatstone bridge is used. The signal is fed into a PC and displayed through LabView software.
This unique introduction to the growing field of microfluidics applied to genomics provides an overview of the latest technologies and emphasizes its potential in answering important biological questions. Written by a physicist and a biologist, it offers a more comprehensive view than the previous literature. The book starts with key ideas in molecular biology, developmental biology and microtechnology before going on to cover the specifics of single cell analysis and microfluidic devices for single cell molecular analysis. Review chapters discuss the state-of-the art and will prove invaluable to all those planning to develop microdevices for molecular analysis of single cells. Methods allowing complete analysis of gene expression in the single cell are stressed - as opposed the more commonly used techniques that allow analysis of only a few genes at a time. As pioneers in the field, the authors understand how critical it is for a physicist to understand the biological issues and questions related to single cell analysis, as well for biologists to understand what microfluidics is all about. Aimed predominantly at graduate students, this book will also be of significant interest to scientists working in or affiliated with this field.
Based on our previous work on the design of pillar array columns for liquid chromatography, we report on a new design for high-efficiency, high loadability gas chromatography columns. The proposed design can either be considered as a packed bed with perfectly ordered and uniform flow paths, or as a multi-capillary columns (8 parallel tracks) distinguishing itself from the conventional multi-capillary variants by ensuring a maximal inter-connectivity between the flow paths to avoid the so-called polydispersity effect (dispersion arising from the inevitable differences in migration velocity between parallel flow paths). Despite our relative inexperience with column coating, and most probably suffering from the same problem of stationary phase pooling in the right-angled corners of the flow-through channels as other chip-based GC devices, the efficiencies obtained in a L=70cm long chip for respectively unretained and retained components went up to N = 60,000 and 36,000 under isothermal conditions. Under programmed temperature conditions, a peak capacity of 170 was obtained in 3.6 min. For retained compounds, the optimal flow rate is found to be on the order of 0.4 mL/min, achieved at an operating pressure of 2.3 bar. Intrinsically, the column combines the efficiency of a 75m capillary with the mass loadability of a 240m capillary.
A microfabricated separation column designed for ultimate use in a wearable gas chromatographic micro-analytical system (μGC) for analyzing mixtures of airborne volatile organic compounds (VOC) is described. The monolithic μcolumn chip measures 7.1 × 2.7 × 0.075 cm and contains a 6-m long, 250 × 140 μm deep-reactive-ion-etched Si channel with a Pyrex cap, wall-coated with a polydimethylsiloxane (PDMS) stationary phase. Along the channel are three serial 2-m long spiral segments, each with an independent integrated resistive heater and thermal isolation features etched in the substrate. By turning the segment heaters on and off at strategic points during a separation, significant energy savings could be realized relative to heating the entire chip simultaneously (i.e., globally), with no loss in chromatographic resolution. A classical lumped element model was used as the basis for simulations of energy consumption, and a published band trajectory model was used to estimate analyte residence times in each segment. Four simple mixtures of volatile organic chemicals were used to evaluate the models and assess the energy consumed for zone heating and global heating under isothermal and temperature-ramped conditions. Results indicate that reductions in the required energy per analysis using zone (vs. global) heating ranged from 14 to 31% among the cases considered, depending on the heating profile (i.e., isothermal or ramped), heating schedule, and the retention times of the analytes in the mixture. Modeled energy reductions tended to underestimate experimental reductions, but differed by <2% in all cases considered. This approach to μcolumn design and operation shows promise for extending battery life in wearable μGC instrumentation.
Purpose
As the concentration of environmental samples was generally very low and existing analytical instruments had limited sensitivity, developing mini pre-treatment systems for effectively concentrating the components was very important and necessary. The purposed of this paper is to develop mini pretreatment system integrated with micro pre-concentrator and micro GC column.
Design/methodology/approach
In this work, a mini pre-treatment system integrated with a micro pre-concentrator and a micro gas chromatograph (GC) column was proposed. The micro pre-concentrator filled with single-walled carbon nanotubes as adsorbent materials was able to effectively concentrate the trace environmental sample, which dramatically improved the response of detectors. In addition, instead of conventional columns, micro GC columns were able to effectively separate gas mixtures, which are able to overcome low resolution and poor anti-interference ability of portable instruments.
Findings
The results demonstrated that the proposed pre-treatment system was able to concentrate the trace sample with a concentration factor of 15 and effectively separate the gas mixtures with a resolution over 1.5.
Originality/value
A mini pre-treatment system integrated with a micro pre-concentrator and a micro GC column was proposed.
In the field of environmental measurement and security, a portable gas chromatograph (GC) is required for the on-site analysis of multiple hazardous gases. Although the gas separation column has been downsized using micro-electro-mechanical-systems (MEMS) technology, an MEMS column made of silicon and glass still does not have sufficient robustness and a sufficiently low fabrication cost for a portable GC. In this study, we fabricated a robust and inexpensive high-precision metal MEMS column by combining diffusion-bonded etched stainless-steel plates with alignment evaluation using acoustic microscopy. The separation performance was evaluated using a desktop GC with a flame ionization detector and we achieved the high separation performance comparable to the best silicon MEMS column fabricated using a dynamic coating method. As an application, we fabricated a palm-size surface acoustic wave (SAW) GC combining this column with a ball SAW sensor and succeeded in separating and detecting a mixture of volatile organic compounds.
This paper reports the development of a new class of high-performance microfabricated separation columns called high-density semi-packed columns (HDSPCs). These columns are realized by using a meter long and 145 μm-wide silicon microchannel design with embedded circular micropillars (15 μm diameters) and 5 μm post spacing (perpendicular to the gas flow). The HDSPCs are coated using our previously developed atomic layer deposition (ALD) based aluminium oxide and silane functionalized thin adsorbent film. Moreover, in this study we optimize both ALD deposition temperature (100 °C, 150 °C, 250 °C and 300 °C) and film thickness (10 nm, 20 nm and 30 nm) using different chromatographic parameters (plate number, peak-to-peak resolution, and separation factor). Additionally, the thermodynamic characteristics of these silane functionalized/ALD films are also studied using Van’t Hoff plots. These columns with optimized stationary phases are able to provide ≈8,000 effective plates/meter and successfully separate a custom made hydrocarbon sample mixture with high peak-to-peak resolution.
We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension ((2)D) to increase the (2)D separation time (up to 32 s) and hence (2)D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the (1)D column to monitor the eluent from (1)D and assist in reconstructing (1)D elution peaks. With the information obtained jointly from the (1)D and (2)D detectors, (1)D elution peaks could be reconstructed with significantly improved (1)D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct (1)D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C6-C12), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.
A new method for separation of 11 n-alkanes: octane, o-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentdecne, n-hexadecath, heptadecane, n-octadecane in soil samples was developed. Kuderna-Danish (K.D.) concentrator enrichment prior to ultrasonic extraction and the silicone chromatography column purification and with gas chromatography flame ionization detection (GC-FID) could be used for n-alkanes determination. The micro channels of open tubular column were fabricated onto a silicon wafer to replace the quartz capillary chromatographic column. The column structure and analysis parameters that affected the column separation were investigated and optimized. Under optimal conditions, the extract reagent was centrifuged and collected. A silicone chromatography column and a K.D. concentrator were used for further clean-up and enrichment. Using this method, the limits of detection (LOD) and limits of quantification (LOQ) were obtained in the range of 0.03–0.15 and 0.1–0.5 mg kg−1 in soil samples, respectively. The relative standard deviation (RSD) was under 12%. The optimized procedure that presented good analytical performance (with recoveries ranging from 56.5% to 89.2%), was successfully applied to determine n-alkane content in farmland soil samples adjacent to a highway. The results showed that the MWCNTs-functionalized column is capable of separating the alkane contaminations with high resolution in about 3 min, which is much shorter than that of GC-MS and other conventional analytical methods, demonstrating its great potential for rapid analysis.
This paper reports the characterization of a miniaturized circulatory column system that is capable of magnifying the effective column length by forming a circulatory loop with chip-scale columns, thus ultimately achieving high-efficiency target separation. The circulatory column system is composed of a tandem of 25 cm microcolumns and six valves for fluidic flow control in order to enable chromatographic separation in circulatory motions while requiring only 5.5 kPa of pressure, which current micropumps are currently capable of supplying. The developed column system (1) successfully demonstrated 16 times elongation of a virtual column length up to 800 cm by only utilizing two 25 cm microcolumns, which is the longest column length reported by any MEMS-scale functioning GC column, (2) achieved a high theoretical plate number of 68 696 with pentane circulating after 15.5 circulatory cycles, which corresponds to the plate number per length-pressure of 1611 plate m(-1) kPa(-1), the highest record reported yet, and (3) demonstrated successful separation of target molecules during circulation by utilizing a pentane/hexane mixture, resulting in magnification of the two corresponding peaks via circulation.
Over 30 years, portable systems for fast and reliable gas analysis are at the core of both academic and industrial research. Miniaturized systems can be helpful in several domains. The way to make it possible is to miniaturize the whole gas chromatograph. Micro-system conception by etching silicon channel is well-known. The main objective is to obtain similar or superior efficiencies to those obtained from laboratory chromatographs. However, stationary phase coatings on silicon surface and micro-detector conception with a low limit of detection remain a challenge. Developments are still in progress to offer a large range of stationary phases and detectors to meet the needs of analytical scientists. This review covers the recent development of micro-gas analyzers. It focuses on injectors, stationary phases, column designs and detectors reported in the literature during the last three decades. A list of commercially available micro-systems and their performances will also be presented.
Within a project exploring the application of lab-on-chip GC to in-field analysis of the plant volatile fraction, this study evaluated the performance of a set of planar columns (also known as microchannels, MEMS columns, or microfabricated columns) of different dimensions installed in a conventional GC unit. Circular double-spiral-shaped-channel planar columns with different square/rectangular sections up to 2m long were applied to the analysis of both essential oils and headspace samples of a group of medicinal and aromatic plants (chamomile, peppermint, sage, rosemary, lavender and bergamot) and of standard mixtures of related compounds; the results were compared to those obtained with reference narrow-bore columns (l:5m, dc:0.1mm, df:0.1μm). The above essential oils and headspaces were first analyzed quali-and quantitatively with planar columns statically coated with conventional stationary phases (5%-phenyl-polymethylsiloxane and auto-bondable nitroterephthalic-acid-modified polyethylene glycol), and then submitted to chiral recognition of their diagnostic markers, by enantioselective GC with a planar columns coated with a cyclodextrin derivative (30% 6(I-VII)-O-TBDMS-3(I-VII)-O-ethyl-2(I-VII)-O-ethyl-β-cyclodextrin in PS-086). Column characteristics and analysis conditions were first optimized to obtain suitable retention and efficiency for the samples investigated. The planar columns tested showed performances close to the reference conventional narrow-bore columns, with theoretical plate numbers per meter (N/m) ranging from 6100 to 7200 for those coated with the conventional stationary phases, and above 5600 for those with the chiral selector.
This paper presents the implementation for the first time of a porous SiOCH thin layer as stationary phase for silicon microcolumns for gas chromatography (GC). Deposition of the hybrid layer was obtained by plasma-enhanced-chemical-vapor-deposition (PECVD) with a porogen approach. Conformal and collective coating of the microcolumns was achieved and BTEX (Benzene, Toluene, Ethyl-benzene, o-Xylene) mixture could be separated with a good efficiency. This new process enables to consider a mass production of efficient microcolumns that is needed for the development of miniaturized, low cost, portable GC systems, e.g. for air quality monitoring.
In this work, a micro packed gas chromatograph column integrated with a micro heater was fabricated by using laser etching technology (LET) for analyzing environmental gases. LET is a powerful tool to etch deep well-shaped channels on the glass wafer, and it is the most effective way to increase depth of channels. The fabricated packed GC column with a length of over 1.6m, to our best knowledge, which is the longest so far. In addition, the fabricated column with a rectangular cross section of 1.2mm (depth)×0.6mm (width) has a large aspect ratio of 2:1. The results show that the fabricated packed column had a large sample capacity, achieved a separation efficiency of about 5800 plates/m and eluted highly symmetrical Gaussian peaks.
This paper presents a novel stationary phase for silicon microfabricated columns for gas chromatographic (GC) separation of light alkanes. Coated columns show an excellent efficiency, up to 8000 theoretical plates per meter and enable complete separation of light isomeric alkanes. An optimized column, with a thicker deposition, even enables the fast separation of a natural gas like mixture of light isomeric alkanes CI to C5 in less than 30 seconds. Copyright © (2013) by the Chemical and Biological Microsystems Society All rights reserved. All rights reserved.
This chapter briefly describes the classical LIGA technique, starting with the mask-making process and ending with the molding technique, with an emphasis on deep X-ray lithography. The main process steps have given the technique its name, LIGA, a German acronym consisting of LI (lithographie for lithography), G (galvanik for electroplating), and A (abformung for replication techniques). LIGA allows for the manufacturing of microcomponents with almost arbitrary lateral geometry and resolution in the micron range, but with structure heights into the millimeter range. A variety of applications have been presented, mostly from the field of micro-optics, but also from other industrial areas that take advantage of LIGA-based microsystem technology. The chapter also describes the standard X-ray lithography process and its characteristics, based on Polymethyl methacrylate (PMMA) as the resist. With the advent of the UV-sensitive SU-8 resist family with its special optical properties, the LIGA concept has been extended to UV lithography, with ultraviolet light replacing the X-rays, followed by subsequent electroplating and molding. This process is known by the names UV-LIGA or poor man's LIGA, the latter because it does not require access to a synchrotron. © 2006 William Andrew Inc. Published by Elsevier Inc. All rights reserved.
Sandia National Laboratories has developed both gas and liquid phase chemical analysis systems. An autonomous hand-held system has been fabricated and demonstrated for sensitive and selective detection of gas phase chemical warfare agents. Recent efforts have focused on maturing this technology and extending its application to other analytical needs. We have now fabricated an on-chip packed gas chromatography column and demonstrated its ability to separate gases such as methane, ethane, ethylene, and acetylene. We have also demonstrated the use of a thermally isolated membrane to rapidly modify and pyrolize fatty acids to form volatile fatty acid methyl esters (FAMEs). This new tool is useful in analyzing biological samples. Finally, we have used rapid temperature ramping of our on-chip open tubular columns to enable separation of low volatility analytes such as explosives and FAMEs. These new capabilities significantly extend the applicability of Sandia’s µChemLab™ technology.
We describe first results from a micro-analytical subsystem that integrates a detector comprising a polymer-coated micro-optofluidic ring resonator (μOFRR) chip with a microfabricated separation module capable of performing thermally modulated comprehensive two-dimensional gas chromatographic separations (μGC × μGC) of volatile organic compound (VOC) mixtures. The 2 × 2 cm μOFRR chip consists of a hollow, contoured SiOx cylinder (250 μm i.d.; 1.2 μm wall thickness) grown from a Si substrate, and integrated optical and fluidic interconnection features. By coupling to a 1550 nm tunable laser and photodetector via an optical fiber taper, whispering gallery mode (WGM) resonances were generated within the μOFRR wall, and shifts in the WGM wavelength caused by transient sorption of eluting vapors into the PDMS film lining the μOFRR cylinder were monitored. Isothermal separations of a simple alkane mixture using a PDMS coated 1(st)-dimension ((1)D) μcolumn and an OV-215-coated 2(nd)- dimension ((2)D) μcolumn confirmed that efficient μGC × μGC-μOFRR analyses could be performed and that responses were dominated by film-swelling. Subsequent tests with more diverse VOC mixtures demonstrated that the modulated peak width and the VOC sensitivity were inversely proportional to the vapor pressure of the analyte. Modulated peaks as narrow as 120 ms and limits of detection in the low-ng range were achieved. Structured contour plots generated with the μOFRR and a reference FID were comparable.
With the help of micro-electromechanical systems (MEMS) and complementary metal-oxide-semiconductor (CMOS) technology, a portable micro gas chromatography ([Formula: see text]) system for lung cancer associated volatile organic compounds (VOCs) detection is realized for the first time. The system is composed of an MEMS preconcentrator, an MEMS separation column, and a CMOS system-on-chip (SoC). The preconcentrator provides a concentration ratio of 2170. The separation column can separate more than seven types of lung cancer associated VOCs. The SoC is fabricated by a TSMC [Formula: see text] 2P4M process including the CMOS VOCs detector, sensor calibration circuit, low-noise chopper instrumentation amplifier (IA), 10 bit analog to digital converter, and the microcontrol unit (MCU). Experimental results show that the system is able to detect seven types of lung cancer associated VOCs (acetone, 2-butanone, benzene, heptane, toluene, m-xylene, 1,3,5-trimethylbenzene). The concentration linearity is [Formula: see text] and the detection sensitivity is up to 15 ppb with 1,3,5-trimethylbenzene.
Semipacked columns (SPCs) with integrated micropillars have been characterized for high chromatographic efficiencies and fast separations. In this article, high-yield and stable alkane thiol based stationary phase coating methods are presented for SPCs. Briefly, a new three step (anisotropic, O2 plasma, and isotropic) etching method is first developed in order to improve metal lift-off by producing a 3-dimensional undercutting profile inside deep etched SPCs. This innovative fabrication scheme is used for 1 m-long, 220 μm-deep, 190 μm-wide SPCs with circular micropillars of 20 μm-diameters and 42 μm-post spacing. Two different thin gold film deposition techniques are utilized for microcolumns (1) a wafer-level physical vapor deposition, and (2) a device level layer-by-layer (LbL) self-assembly of gold nanoparticles (3.2 nm diameter). After gold film deposition and metal lift-off, the surface of the patterned gold layer is functionalized with a 2 mM octadecanethiol (C18H37SH) solution for chromatographic separations. Both kinetic (Golay plots) and thermodynamic (Van’t Hoff plot) properties of thiol-functionalized gold phases are studied. The significance of SPCs, for faster analysis, is also validated by achieving baseline separation of a straight chain alkane mixture, containing high boilers (174 °C to 287 °C), within 45 s.
We present for the first time a proof-of-concept system implementing the stochastic injection techniques within a silicon-based micro gas chromatograph (µGC) which differs from standard laboratory chromatographs by its small size, shorter column and corresponding elution times, and potential low cost when batch manufactured in high volumes. We demonstrate that stochastic injection techniques can enable the continuous detection of pollutants or toxic gases, with high temporal resolution (5 seconds) and order-of-magnitude improvements in limit of detection compared to a standard single-injection technique, thus greatly improving performance of air quality monitoring devices. Since micro-GC systems have the potential to one day become ubiquitous in indoor environments, such stochastic injection techniques could enable faster detection of toxic compounds at lower concentrations in both industrial and residential settings.
In recent years, the need of measurement and detection of samples in situ or with very small volume and low concentration (low sub parts per billion) is a cause for going to miniaturize systems via micro electromechanical system (MEMS) technology. Gas chromatography (GC) is a common technique that is widely used for separating and measuring the semi volatile and volatile compounds. Conventional GCs are bulky and cannot be used for in situ analysis, hence in the last decades many studies have been reported with the aim of designing and developing chip-based GC. The focus of this review is to follow and investigate the development and the achievements in the field of chip-based GC and its components from beginning up to now.
In this paper, two configurations of columns were designed for gas chromatography (GC) analysis, and the effect of airflow rate in the corners of GC channel was simulated using ANSYS dynamic analysis. The difference of airflow rate between in the corners of serpentine channel and in the gas inlet reaches 3.13 cm/s, and the changes in the distribution of airflow rate in the corners of serpentine channel are obvious and relatively large. However, the difference of airflow rate between in the corners of spiral channel and in the gas inlet is only 1.33 cm/s. Moreover, the distribution of airflow rate in the spiral channel is relatively uniform. Then, these GC columns were fabricated based the Micro-Electro–Mechanical-Systems (MEMS) technologies and coated the stationary phase using a dynamic coating procedure. The spiral channel GC columns showed excellent overall separation performance with excellent chromatographic peaks, and the spiral channel GC columns separated the gaseous mixture with a resolution of 10.97 and yielded about 3900 theoretical plates.
The first molded gas chromatography (GC) microcolumn is described. This microcolumn consists of a single microtextured thermoset polymer composite which acts as both the structural material and the stationary phase. The resultant microcolumn is inexpensive and has been coupled to a disposable colorimetric sensor array, creating a disposable column-detector unit and demonstrating a proof of concept for a disposable GC microcolumn.
A polydimethylsiloxane micromolded separation column is presented with monolithically integrated gas injection, temperature control, and a nanomaterial chemiresistor array for multiparametric gas detection in complex mixtures on a unique single chip platform. Sensor arrays are made of carbon nanotubes, vanadium oxide, and reduced graphene oxide nanomaterials. The functionality of a micromolded gas separation device as opposed to the conventional etched silicon GC column opens the door to disposable, easily manufactured, stand-alone gas chromatography for clinical diagnostics or remote fieldwork. Combining separation column with a diverse nanomaterial sensor array provides multiparametric detection of gases in a single chip device. The device has the dimensions of a glass slide while drawing <2 W of power and capable of separation and detection of gases verified using a standard analytical mixture of aliphatic compounds.
In this paper, micro gas chromatography columns were fabricated through the micro-electro-mechanical system (MEMS) technique. Two types of columns were designed, namely, open-tube and semi-packed columns. By comparing different structures, column efficiency was improved by embedding square posts in the channel to form a semi-packed column. The result showed that column efficiency of the semi-packed column reached 55366 plates per m. This study was the first to report based on experimentation that MEMS-based columns can reach a plate number this high. The plate number was five times higher than the value previously reported. In addition, a 30 m-long Agilent HP-5 commercial capillary column was used to compare the results with findings obtained using a MEMS-based semi-packed column. The analytes were perfectly separated in both columns. The column efficiency of the HP-5 capillary column was 5490 plates per m, which was 10 times lower than that of the micro-fabricated, semi-packed column.
Using a large-capacity-on-chip preconcentrator device for selective ethylene measurement leads to some challenges. The dramatic increase of the water influence and the gas chromatography effect of the preconcentrator must be known and compensated before a good measurement with this new device can be performed. Nevertheless, after facing these challenges the small gas chromatograph presented in this paper was for the first time able to detect an ethylene concentration of 170 ppbv. Deduced from this measurement a detection limit below 50 ppbv can be reached, which is absolutely mandatory for shelf life prediction of climacteric fruits. New stationary phases were tested. The used packed gas chromatography column is now capable of separating vaporized water and ethylene gas from each other, which was a breakthrough in the analysis of ethylene concentrations in ambient air. It can be predicted that the system will be available at a price under 1000 (sic). (C) 2014 Published by Elsevier B.V.
A static coating procedure for open tubular (capillary) columns in glass is described and the performance of the column is compared with that of commercially available open tubular columns. Conventional coating efficiencies of 30 to 85% of the maximum possible value are attained in glass capillary columns. This is better than the values obtained with dynamic methods for coating glass capillaries.
The development and characterization of a microanalytical subsystem comprising Si-micromachined first- and second-dimension separation columns and a Si-micromachined thermal modulator (μTM) for comprehensive two-dimensional (i.e., µGC × µGC) separations is described. The first dimension consists of two series coupled 3.1 × 3.1 cm μcolumn chips with etched channels 3-m long and 250 × 140 μm in cross section, wall-coated with a PDMS stationary phase. The second dimension ((2)D) consists of a 1.2 × 1.2 cm μcolumn chip with an etched channel 0.5-m long and 46 × 150 μm in cross section wall-coated with either a trigonal tricationic room-temperature ionic liquid (RTIL) or a commercial poly(trifluoropropylmethyl siloxane) (OV-215) stationary phase. The 2-stage, cryogen-free μTM consists of a Si chip containing two series coupled, square spiral channels 4.2 and 2.8 cm long and 250 × 140 µm in cross section wall-coated with PDMS. Conventional injection methods and flame ionization detection were used. Temperature-ramped separations of a simple alkane mixture using the RTIL-coated (2)D µcolumn produced reasonably good peak shapes and modulation numbers; however, strong retention of polar compounds on the RTIL-coated (2)D μcolumn led to excessively broad peaks with low (2)D resolution. Substituting OV-215 as the (2)D μcolumn stationary phase markedly improved the performance, and a structured 22-min chromatogram of a 36-component mixture spanning a vapor pressure range of 0.027 to 13 kPa was generated with modulated peak fwhm values ranging from 90 to 643 ms and modulation numbers of 1-6.
Fabrication technologies for microelectromechanical systems (MEMS) allow miniaturization of conventional benchtop gas chromatography (GC) to portable, palm-sized microfabricated GC (μGC) devices, which are suitable for on-site chemical analysis and remote sensing. The separation performance of μGC systems, however, has not been on par with conventional GC. Column efficiency, peak symmetry and resolution are often compromised by column defects and non-ideal injections. The relatively low performance of μGC devices has impeded their further commercialization and broader application. In this work, the separation performance of μGC columns was improved by incorporating thermal gradient gas chromatography (TGGC). The analysis time was ∼20% shorter for TGGC separations compared to conventional temperature-programmed GC (TPGC) when a wide sample band was introduced into the column. Up to 50% reduction in peak tailing was observed for polar analytes, which improved their resolution. The signal-to-noise ratios (S/N) of late-eluting peaks were increased by 3-4 fold. The unique focusing effect of TGGC overcomes many of the previous shortcomings inherent in μGC analyses.
Copyright © 2014. Published by Elsevier B.V.
This paper reports an integrated microscale gas chromatography (mu GC) system, the iGC1, which contains four components: 1) a Knudsen pump (KP); 2) a preconcentrator-focuser (PCF); 3) a separation column; and 4) a gas detector. All four components are fabricated from glass wafers using a three-mask process with minimal postprocessing. In a stackable architecture, the components are finally assembled into a 4-cm(3) system. The stacked iGC1 system demonstrates the successful separation and detection of an alkane mixture in the range of C-5-C-8 in less than 60 s. [2013-0230]
We report on a small (20 × 10 mm) micromachined device for the detection of gases in micro-gas chromatography (GC). It incorporates a micro-discharge across a 20-μm gap, and a remote electrode in the micro cavity that generates an electrical signal corresponding to the photo-ionization of gaseous analytes in a stream of carrier gas. Multi-component mixtures were detected and the results compared to those obtained with a flame ionization detector. The minimum detectable limit is 350 pg.μL−1 of n-octane in air when applying a 1.4 mW discharge. The combination of wet etching of glass (as used for microfluidic channels) with a lift-off process for detector electrodes by a robust batch process results in a universal, non-destructive, and sensitive microdetector for micro-GC.
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