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Compensation of the baseline temperature fluctuations for autonomous CE-C4D instrument working in harsh environments
Abstract
One of the main problems of the remote complex sample analysis instrumentation is that such systems are susceptible to temperature fluctuations. Temperature regulation is energetically ineffective, and it is not used in most of the field portable analytical systems. Separations performed in a changing temperature environment provide electropherograms with considerable baseline fluctuations, resulting in significant errors in detection and integration of the peaks. This paper describes electropherogram baseline compensation that is suitable for the capillary electrophoresis ‐ contactless conductivity detection analytical method. The baseline compensation utilizes linear or polynomial data processing methods, and can be programmed in‐line using simple microcontroller, or on‐line and off‐line in data acquisition software. This method is targeted for field portable and autonomous analytical systems that are utilized in a fluctuating environment.
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... In numerous cases, those instruments are supplied with electrokinetic sample injection or passive siphon effect sample injection. [19][20][21] Hydrodynamic injection in portable CE instrumentation is rarer due to difficulties designing it, but it has already been reported by several authors. [22][23][24] Although sequential injection in CE utilizing high-performance liquid chromatography selector or injector valves signicantly extends the weight of the instrument, it is still useful in some portable applications. ...
... 25,26 Depending on what analytes of interest are, CE and ME is supplied with different detectors: (a) uorescence, (b) contactless conductivity, (c) electrochemical. 19,20,[27][28][29][30][31] Depending on the application, use-cases of portable CE instruments range from point-of-care analysis to the detection of explosives and other potentially hazardous compounds. 12,21,[32][33][34][35][36] Some attempts to design and apply autonomous analytical systems have been performed. ...
... Data analysis was done using previously programmed soware. 19 We designed CE system frame parts using open-source soware FreeCAD (http:// www.freecadweb.org/) and 3D printed them using the Makerbot Z18 3D printer (Makerbot, USA). ...
Hazardous remote places exist in the world. Why should health or life be risked sending a scientist to the investigation site, as the remote analytical instrumentation exists? Different scientific fields require instruments that could be used on-site (in situ), therefore the purpose of this work was to design a fully automated chemical analysis system small enough to be mountable on a drone. Here we show an autonomous analytical system with sampling capability on a drone. The system is suited for the remote and autonomous analysis of volatile and non-volatile chemicals in the air. The designed system weighs less than 800 g. Data are transmitted wirelessly. Collected substances are separated automatically without the intervention of the operator using the method of capillary zone electrophoresis. The analytes are detected using a miniaturized contactless conductivity detector quantifying them down to less than 1 μM. In this work, we demonstrated sampling and separation of volatile amines (triethylamine and diethylamine) and organic acids (acetic and formic acids), non-volatile inorganic cations (K⁺, Ca²⁺, Na⁺), and protein (bovine serum albumin) in the aerosol state. It was shown that the capillary electrophoretic analysis can be performed on a hovering drone. We anticipate our work to be a starting point for more sophisticated, autonomous complex sample analysis. We believe that our designed instrument will enable the investigation of hazardous places in different research fields.
... The analysis that can be performed in situ provides several advantages: (i) reduces analysis errors due to the fact that sample transportation is not needed, and chemical degradation is avoided, and (ii) reduces the duration of the total analytical process [5]. Several chemical analyftical techniques have been applied, or are being developed for field-portable or autonomous applications: (i) liquid chromatography [6,7], (ii) capillary electrophoresis [8][9][10][11], (iii) digital microfluidics [12] and (iv) electrochemical analysis [13]. Designing portable or autonomous instruments can be problematic due to the following reasons: (i) such instrumentation has the limited battery power supply, (ii) a low number of mechanical and moving parts must be used in the design, and (iii) such instrumentation is susceptible to changing environment and especially temperature fluctuations [10,14]. ...
... Several chemical analyftical techniques have been applied, or are being developed for field-portable or autonomous applications: (i) liquid chromatography [6,7], (ii) capillary electrophoresis [8][9][10][11], (iii) digital microfluidics [12] and (iv) electrochemical analysis [13]. Designing portable or autonomous instruments can be problematic due to the following reasons: (i) such instrumentation has the limited battery power supply, (ii) a low number of mechanical and moving parts must be used in the design, and (iii) such instrumentation is susceptible to changing environment and especially temperature fluctuations [10,14]. ...
... During the development of the instrument 3 models were made (Fig. 1). The first model was equipped with a LED of a single wavelength and wired (USB cable) connectivity, the second model was upgraded with 3 different colour LEDs, and the third model, together with the above-mentioned upgrades, had a possibility of wireless communication using an NRF24L01+ wireless transmitter (Nordic Semiconductor, Norway) [10]. ...
Portable and autonomous analytical instrumentation is becoming more important. Portable instrumentation can be designed via the miniaturization approach and this is a challenging task due to: (i) the limited battery power supply, (ii) a low number of mechanical and moving parts allowed in the design and (iii) susceptibility to changing environment and temperature fluctuations. In this work we describe the design of a light emitting diode (LED) based 3D printed miniaturized colorimeter (dimensions: 5 cm × 4 cm × 4.5 cm (length, width, height), weight less than 56 g). The colorimeter was optimized for determination of the total phenolic compound content, the total flavonoid content and radical scavenging activity. The designed instrument provides comparable results to those of a conventional desktop spectrophotometer existing on the market. The designed LED based miniaturized colorimeter has wireless communication capability. This work demonstrates that this instrument can be applied investigating real samples.
... This leads to variations in the migration times, which is a serious disadvantage of the portable CE instrument, because migration time is the only parameter that can be used for sample component identification. Compensation for the baseline variations due to fluctuations of the ambient temperature for autonomous CE-C4D instruments (working in harsh environments) could be accomplished by analysis and compensation of the baseline [48]. In addition, this problem can be eased more precisely using a high-voltage-compatible flow sensor, capable of monitoring the volumetric flow inside the capillary during separation [49]. ...
... To allow for the mechanical mounting and rotation of the system in these experiments, another instrument in development with a shorter capillary (L tot 50 cm, L eff 40 cm) and a 10 kV separation voltage was used. Peak migration times were adjusted based on any parasitic siphoning flows, similar to the independent reservoir rotation tests, via active flow monitoring [26], and temperature-induced baseline fluctuations in the data were compensated using a previously published procedure [27]. Overall, these results demonstrate that the reservoirs are not affected by the orientation of the gravity vector, and because they are single-phase, would behave suitably under microgravity conditions. ...
Capillary electrophoresis (CE) holds great promise as an in situ analytical technique for a variety of applications. However, typical instrumentation operates with open reservoirs (e.g., vials) to accommodate reagents and samples, which is problematic for automated instruments designed for space or underwater applications that may be operated in various orientations. Microgravity conditions add an additional challenge due to the unpredictable position of the headspace (air layer above the liquid) in any two-phase reservoir. One potential solution for these applications is to use a headspace-free, flow-through reservoir design that is sealed and connected to the necessary reagents and samples. Here we demonstrate a flow-through HV reservoir for capillary electrophoresis that is compatible with automated in situ exploration needs, and which can be electrically isolated from its source fluidics (in order to prevent unwanted leakage current). We also demonstrate how the overall system can be rationally designed based on the operational parameters for CE to prevent electrolysis products produced at the electrode from entering the capillary and interfering with the CE separation. A reservoir was demonstrated with a 19 mm long, 1.8 mm inner diameter channel connecting the separation capillary and the HV electrode. Tests of these reservoirs integrated into a CE system show reproducible CE system operation with a variety of background electrolytes at voltages up to 25 kV. Rotation of the reservoirs, and the system, showed that their performance was independent of the direction of the gravity vector. This article is protected by copyright. All rights reserved.
... This is a serious disadvantage of a portable CE instrument with optical or electrochemical detectors because the migration time is the only parameter that can be used for sample component identification. Compensation of the baseline temperature fluctuations for autonomous CE-C4D instru-ments (working in harsh environments) could be done by analysis and compensation of the baseline [46]. In addition, this problem can be alleviated more precisely by using a high-voltage-compatible flow sensor capable of monitoring the volumetric flow rate inside the capillary during a separation. ...
Most of the publications in green analytical chemistry (GAC) deal with the benign solvents and procedures and all aspects of measures of the greenness of certain methods. The equally important instrumentation aspects in GAC have received much less attention. Instruments in contemporary analytical chemistry have a significant footprint. Capillary electrophoresis (CE) is a technology that offers an instrument whose ecological footprint could be much less than that of other popular analytical technologies. This paper describes the GAC features of CE with many examples. Those green features of CE include the capability of miniaturization and, thus, the possibility of making portable instruments that can be used in situ. In recent years, many groups have demonstrated increasing interest in developing simple, robust, and inexpensive portable CE instruments. This paper will address aspects of CE associated with portability, open access instrumentation, and prospects of CE for citizen science. The extensive use of items provided by the electronic and computer industry contributes to this trend.
... For the compensation of the baseline drift due to temperature fluctuations, a different algorithm has been developed. 43 If a uniform averaging window size is used for the whole electropherogram, nonoptimal signal filtering is obtained if: (i) the averaging window size is too small, then the noise is still visible in the electropherograms (as demonstrated for moving average, FFT and Savitzky−Golay filters ( Figure 4G−I)) and (ii) if the averaging window size is too high, moving average algorithm distorts peaks and corrupts the information (as demonstrated for moving average, FFT, and Savitzky−Golay filters ( Figure 4D−F)). ...
In the present work we demonstrate the novel approach to improve the sensitivity of the “out of lab” portable capillary electrophoretic measurements. Nowadays, many enhancement methods are: (i) underused (non-optimal), (ii) overused (distorts the data), or (iii) inapplicable in field-portable instrumentation due to lack of computational power. Described innovative migration velocity-adaptive moving average method uses optimal averaging window size and can be easily implemented with microcontroller. The contactless conductivity detection was used as a model for the development of a signal processing method and the demonstration of its impact on the sensitivity. The frequency characteristics of the recorded electropherograms and peaks were clarified. Higher electrophoretic mobility analytes exhibit higher frequency peaks, while lower electrophoretic mobility analytes exhibit lower frequency peaks. Based on obtained data, a migration velocity-adaptive moving average algorithm was created, adapted and programmed into capillary electrophoresis data processing software. Employing the developed algorithm, each data point is processed depending on a certain migration time of the analyte. Because of the implemented migration velocity-adaptive moving average method the signal-to-noise ratio improved up to 11 times for sampling frequency of 4.6 Hz and up to 22 times for sampling frequency of 25 Hz. This paper could potentially be used as a methodological guideline for the development of new smoothing algorithms that require adaptive conditions in capillary electrophoresis, and other separation methods.
Over the past three decades, microchip electrophoresis coupled with capacitively coupled contactless conductivity detection (ME-C4D) has garnered considerable interest due to its various merits, including minimal sample consumption, compact structure, immediate detection, and high analytical precision. Continuous technological innovation and improvement have significantly advanced ME-C4D in structural design, fabrication processes, and experimental methodologies. As a result, the application of this technology has expanded into a wider range of electrochemical analysis fields, including disease diagnosis, food safety assessment, environmental pollutant detection, and soil nutrient analysis. This review meticulously examines the forefront of ME-C4D over the last five years. It methodically categorizes and scrutinizes advancements from various dimensions, including newly emerged ME microchips, C4D electrodes, experimental protocols, and pioneering applications. Moreover, this paper critically summarizes these developments, identifying the prevailing limitations and challenges within ME-C4D. Ultimately, it projects potential future trajectories for innovation in the field of ME-C4D, suggesting pathways to overcome existing hurdles and hinting at the untapped possibilities that lie ahead.
A compact CE-C ⁴ D instrument with trace analysis sensitivity ( e.g. 1 ppb or 20 nM level for common inorganic ions) without the need for preconcentration methods has been successfully developed.
A compact, inexpensive sampler instrument for portable capillary electrophoresis (CE) was developed and tested to monitor common inorganic ions in drinking water samples. The sampler uses peristaltic and vacuum pumps and pinch and check valves to control liquid flows. The paper also addresses various aspects of CE associated with portability, open access instrumentation and prospects of CE for citizen science. The extensive use of items provided by the electronic and computer industry contributes to this trend.
This work introduces new hardware configurations for a capacitively coupled contactless conductivity detector (C4D) based on capacitance‐to‐digital conversion (CDC) technology for capillary electrophoresis (CE). The aim was to improve sensitivity, handling, price, and portability of CDC‐based C4D detectors (CDCD) to reach LODs similar to classic C4Ds with more sophisticated electric circuits. To achieve this, a systematic study on the CDCDs was carried out including a direct comparison to already established C4D setups. Instrumental setups differing in electrode lengths, measurement modes and amplification of excitation voltages were investigated to achieve LODs for alkali metal ions of 4 to 12 μM, similar to LODs obtained by classic C4D setups. Lowest LODs were achieved for a setup with two 10 mm electrodes at a distance of 0.2 mm and an excitation voltage of 24 V. The detection head was exceptionally lightweight with only 2.6 g and covered only 20 mm of the capillary on total. This allows multiple detectors along the separation path to enable spatial tracking of analytes during separation. The entirely battery‐powered detector assembly weighs less than 200 g, and the data are transmitted wirelessly for possible portable applications. The hardware and software were optimized for fully automated measurements with real‐time data plotting and allowed multi‐detector setups. The new developments were applied to quantify the potassium salt of glyphosate in its herbicide formulation. This article is protected by copyright. All rights reserved
The developments of analytical contactless conductivity measurements based on capacitive coupling over the two years from mid-2018 to mid-2020 are covered. This mostly concerns applications of the technique in zone electrophoresis employing conventional capillaries and to a lesser extent lab-on-chip devices. However, its use for the detection in several other flow-based analytical methods has also been reported. Detection of bubbles and measurements of flow rates in two-phase flows are also recurring themes. A few new applications in stagnant aqueous samples, e.g. endpoint detection in titrations and measurement on paper-based devices, have been reported. Some variations of the design of the measuring cells and their read-out electronics have also been described.
In this work, the design and characterization of a multi-cell capacitively coupled contactless conductivity detection are described. The operation and simultaneous acquisition from 3 detector cells were demonstrated, however, the system is capable of supplying 8 detection cells and can be easily upgraded to maintain 64 capacitively coupled contactless conductivity detection cells. Performing flow-injection analysis, the system recorded as low as 0.01 mM of acetic acid, phosphoric acid, NaH2PO4, and Na2B4O7 solutions in water. The instrument was also capable of recording and distinguishing different mixtures of organic solvents: (a) methanol-acetonitrile, (b) hexane-acetone. The designed detection system is expected to be used coupled with multi-channel separation devices for monitoring of simultaneous processes.
The development of the instrument which will significantly ease the in situ samplings of volatile compounds is described. The purpose of this work was to design an automated, portable, handheld sample collection device that operates with monolithic adsorbents. The sampler contains two lithium-ion batteries, collects samples into micro-liter range volume vials, is supplied with a changeable 100 µm inner diameter six cm long capillary with an in-tube monolithic solid-phase micro-extraction adsorbent. Modeling experiments with triethylamine and diethylamine demonstrated that instrument captured samples containing volatile substances in the range of 3.5 to 118 ppm concentration levels in the air. The substances have been analyzed using a dedicated capillary electrophoresis contactless conductivity detection system and determined amounts of volatile substances in the sample solutions ranged between 3.4 and 1010 µM. Only 0.44 mL of air was enough to adsorb substances on the adsorbent, collecting them into 50 µL of water and achieving a preconcentration effect. The developed instrument is expected to find it’s applications where sampled air or gas volume is in µL – mL range: (a) collection of volatile substances near single plant parts in vivo, (b) collection of beetle pheromones in vivo, (c) volume-restricted machinery and other related applications.
The methodology described in this paper will significantly reduce the time required for understanding the relations between chromatographic data and bio-activity assays. The methodology is a hybrid of hypothesis based and data-driven scientific approaches. In this work, a novel chromatographic data segmentation method is proposed, which demonstrates the capability of finding what volatile substances are responsible for antiviral and cytotoxic effects in the medicinal plant extracts. Up to now the full potential of the separation methods has not been exploited in the life sciences. This was due to the lack of data ordering methods capable to adequately preparing the chromatographic information. Furthermore, the data analysis methods suffer of multidimensionality requiring a large number of investigated data points. A new method is described for processing any chromatographic information into a vector. The obtained vectors of highly complex and different origin samples can be compared mathematically. The proposed method, efficient with relatively small sized datasets, does not suffer of multidimensionality. In this novel analytical approach, the samples did not need fractionation and purification, what is typically used in hypothesis based scientific research. All investigations were performed using crude extracts possessing hundreds of phyto-substances. The antiviral properties of medicinal plant extracts were investigated using gas chromatography-mass spectrometry, antiviral tests and proposed data analysis method. The findings suggested that: (i) beta-cis-caryophyllene, linalool, eucalyptol possess antiviral activity, while (ii) thujone does not, and (iii) alpha-, beta-thujones, cis-p-menthan-3-one, estragole show cytotoxic effects.
The axial C4D (Capacitively Coupled Contactless Conductivity Detection) measurement electronics for capillary electrophoresis is considered and a new improved C5D compensated detection concept is proposed and tested. Using the idle compensation channel with inversed signal and immediate analogue summation of the active and idle channel currents yields effective suppression of the influence of the parasitic stray capacitance. Preliminary experiments have confirmed at least three-fold improvements of measurement resolution. Realisation of electronics allows flexible tuning of frequency from 0.2 MHz to 2 MHz. The relatively high voltage supply of 15 V for the AC measurement units together with 24-bit accurate analogue-to-digital converter yields additional improvement for the sensitivity. © 2016, Kauno Technologijos Universitetas. All rights reserved.
Although simple equivalent circuits have been used to explain the basic functioning of a capacitively coupled contactless conductivity detector (C4D), more sophisticated models are required to take into account the effects of the spatial non-homogeneity of the solution conductivity as the electrophoretic zones pass inside the detector. The overshooting phenomenon observed in real electropherograms may be explained by modeling the coupling of the electrodes with the inner capillary with a network of resistors and capacitors and its dependence with the stray capacitance becomes evident. An even more detailed model of the cell based on electrostatics allows one to calculate the stray capacitances. For the typical geometries and materials, this capacitance is on the order of a few to hundreds of femtofarads. It was possible to demonstrate that the ground plane, sometimes used, reduces the capacitance, but does not eliminate it completely. Possible noise sources are also discussed. The electrode tightness minimizes a possible source of mechanical noise due to variation of the coupling capacitances. Thermal control should also be ensured; the calculations showed that a temperature fluctuation as low as 7×10−3 °C induces artifacts as high as the limit of quantification of K+ in a typical electrophoretic condition, for which the technique has one of its highest sensitivities.
In the present work we demonstrate the novel approach to improve the sensitivity of the “out of lab” portable capillary electrophoretic measurements. Nowadays, many enhancement methods are: (i) underused (non-optimal), (ii) overused (distorts the data), or (iii) inapplicable in field-portable instrumentation due to lack of computational power. Described innovative migration velocity-adaptive moving average method uses optimal averaging window size and can be easily implemented with microcontroller. The contactless conductivity detection was used as a model for the development of a signal processing method and the demonstration of its impact on the sensitivity. The frequency characteristics of the recorded electropherograms and peaks were clarified. Higher electrophoretic mobility analytes exhibit higher frequency peaks, while lower electrophoretic mobility analytes exhibit lower frequency peaks. Based on obtained data, a migration velocity-adaptive moving average algorithm was created, adapted and programmed into capillary electrophoresis data processing software. Employing the developed algorithm, each data point is processed depending on a certain migration time of the analyte. Because of the implemented migration velocity-adaptive moving average method the signal-to-noise ratio improved up to 11 times for sampling frequency of 4.6 Hz and up to 22 times for sampling frequency of 25 Hz. This paper could potentially be used as a methodological guideline for the development of new smoothing algorithms that require adaptive conditions in capillary electrophoresis, and other separation methods.
Concern about the environment is increasing and so is the search for analytical methods that make continuous monitoring possible. Microfluidic devices such as lab-on-a-chip emerge as an alternative to the laboratory-based conventional techniques, making possible the development of unmanned monitoring tools. This review covers the last five years on the application of autonomous microfluidic devices for continuous environmental monitoring and addresses the existing demands in this field.
We describe an open tubular ion chromatograph (OTIC) that uses anion exchange latex coated 5 μm radius silica and 9.8 μm radius poly(methyl methacrylate) tubes and automated time/pressure based hydrodynamic injection for pL-nL scale injections. It is routinely possible to generate 50 000 plates or more (up to 150 000 plates/m, columns between 0.3 and 0.8 m have been used), and as such, fast separations are possible, comparable to or in some cases better than the current practice of IC. With an optimized admittance detector, nonsuppressed detection permits LODs of submicromolar to double digit micromolar for a variety of analytes. However, large volume injections are possible and can significantly improve on this. A variety of eluents, the use of organic modifiers, and variations of eluent pH can be used to tailor a given separation. The approach is discussed in the context of extraterrestrial exploration, especially Mars, where the existence of large amounts of perchlorate in the soil needs to be confirmed. These columns can survive drying and freezing, and small footprint, low power consumption, and simplicity make OTIC a good candidate for such a mission.
We describe an admittance detector for high impedance systems (small capillary bore and/or low solution specific conductance). Operation in the low frequency range (<1 kHz, much lower than most relevant publications) provides optimum response to conductance changes in capillaries <20 μm in bore. The detector design was based on studies described in a preceding companion paper (ref). The highest S/N for detecting 100 μM KCl (5.5 M peak concentration, ~0.8 S/cm) injected into water flowing through a capillary of 7.5 m inner radius (r) was observed at 500-750 Hz. A low bias current operational amplifier in the transimpedance configuration permitted high gain (1 V/nA) to measure pA-nA level currents in the detection cell. Aside from an oscillator, only one more chip, a RMS-DC converter that can also provide offset, formed the complete detection circuitry; an optional additional operational amplifier can provide for added gain and further offset capabilities. Limits of detection (LODs) of KCl scaled inversely with the capillary cross section and were 2.1 and 0.32 μM injected KCl for r = 1 and 2.5 μm capillaries, respectively. Used as a detector on an r = 8 μm bore polymethylmethacrylate capillary in a split effluent stream from a suppressed ion chromatograph, the LOD was 27 nM bromide (Vex 22 V p-p), compared to 14 nM observed with a commercial bipolar pulse macroscale conductivity detector with an actively thermostated cell. We also show applications of the detector in electrophoresis in capillaries with r = 1 and 2.5 μm. Efficient heat dissipation permits high concentrations of the background electrolyte and sensitive detection because of efficient electrostacking.
Techniques that have been variously termed oscillometric detection or (capacitively coupled) contactless conductivity detection (C4D) are known actually to respond to the admittance. It is not often appreciated that the frequency range (f) over which such systems respond (quasi)linearly with the cell conductance decreases acutely with increasing cell resistance. Guidance on optimum operating conditions for high cell resistance, such as for very small capillaries/channels and/or solutions of low specific conductance (), is scant. Several theoretical models exist but none take the capacitance of the solution being measured into account. At high frequencies and low values, much of the current passes through the solution behaving as a capacitor and the capacitance is not very dependent on the exact solution capacitance, resulting in poor, zero, or even negative response. We investigated, both theoretically and experimentally capillaries of inner radii 5-160 μm and = ~1-1400 μS/cm, resulting in cell resistances of 51 G-176 k. A 400-element discrete model was used for simulating the behavior. As model inputs, both the wall capacitance and the stray capacitance were measured. The solution and leakage capacitances were estimated from extant models. The model output was compared to the measured response of the detection system over broad ranges of f and . Other parameters studied include capillary material and wall thickness, electrode spacing and length, Faraday shield thickness, excitation wave forms and amplitude. The simulations show good qualitative agreement with experimental results and correctly predict the negative response behavior observed under certain conditions. We provide optimum frequencies for different operating conditions.
Separation science in harsh environments emerges as a new exciting field of research.•Emphasis should be put on a holistic approach for portable and in situ CE instrumentation design.•Influence of extreme temperatures on separation instruments/protocols have been understood, as well as ways of tackling extreme temperatures.•Gaps in the literature point out that attention to the influence of shock/vibration and extreme ambient pressures on instrument performance is required.•In general, the methods of dealing with the shocks and vibrations are known theoretically but it is not well known how those measures block the vibration and shock influence in reality.
The capacitance-to-digital single chip detector was upgraded. The paper discusses hardware issues and benefits of the designed/ upgraded detector. The device can be operated from rechargeable lithium-ion battery as stand-alone, portable system and is capable of transmitting real-time data wirelessly. The detector and additional modules (battery, battery holder, microcontroller board, wireless module) weight is less than 85 g. Electrophoretic separation in low conductivity 20 mm MES/ L-His buffer, pH 6.1, was performed in order to evaluate detection parameters. The system is capable of quantification of potassium ions down to 0.31 μM. Investigation of differential signal acquisition configuration showed improved performance regarding external noise and temperature fluctuations. The system can be a solution for stand-alone, field-portable capillary format separation detector.This article is protected by copyright. All rights reserved
A capacitance-to-digital converter integrated circuit was implemented in an automated capillary electrophoresis device as a single chip detector. In this paper, design and hardware issues related to the fabrication and application of a miniature detector for contactless measurement of complex impedance are discussed. The capacitance-to-digital converter integrated circuit was used as the whole detector. The advantage of this setup is that the single integrated circuit provides digital data and neither additional signal conditioning nor analog-to-digital converter is required. Different separation conditions were used to evaluate the detection characteristics of the constructed detection unit. A 1 μM limit of detection for sodium and a 1.6 μM limit of detection for potassium ions were revealed for the detector. The detection system designed is competitive with miniaturized contactless conductivity detectors or UV absorbance detectors with respect to overall parameters (sensitivity, resolution, power consumption properties and size). The obtained separation and detection results show that such detection technique can be used as an extremely low power consuming and space saving solution for capillary electrophoresis detection with potential applications in environmental monitoring, process control and various analytical measurements. This article is protected by copyright. All rights reserved
A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of post-blast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual-opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from post-blast residues using an optimized separation electrolyte composed of 20 mM 2-[N-morpholino]ethanosulfonic acid, 20 mM L-histidine , 30 μM cetyltrimethylammonium bromide and 2 mM 18-crown-6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive. This article is protected by copyright. All rights reserved.
The search for signs of life on extraterrestrial planetary bodies is among NASA's top priorities in Solar System exploration. The associated pursuit of organics and biomolecules as evidence of past or present life demands in situ investigations of planetary bodies for which sample return missions are neither practical nor affordable. These in situ studies require instrumentation capable of sensitive chemical analyses of complex mixtures including a broad range of organic molecules. Instrumentation must also be capable of autonomous operation aboard a robotically controlled vehicle that collects data and transmits it back to Earth. Microchip capillary electrophoresis (μCE) coupled to laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant organics while offering low mass, volume, and power requirements. Thus, this technology would be ideally suited for in situ studies of astrobiology targets, such as Mars, Europa, Enceladus, and Titan. In this review, we introduce the characteristics of these planetary bodies that make them compelling destinations for extraterrestrial astrobiological studies, and the principal groups of organics of interest associated with each. And although the technology we describe here was first developed specifically for proposed studies of Mars, by summarizing its evolution over the past decade, we demonstrate how μCE-LIF instrumentation has become an ideal candidate for missions of exploration to all of these nearby worlds in our Solar System.
Capacitively coupled contactless conductivity detection (C4D) is presented in a progressively detailed approach. Through different levels of theoretical and practical complexity, several aspects related to this kind of detection are addressed, which should be helpful to understand the results as well as to design a detector or plan experiments. Simulations and experimental results suggest that sensitivity depends on: 1) the electrolyte co-ion and counter-ion; 2) cell geometry and its positioning; 3) operating frequency. Undesirable stray capacitance formed due to the close placement of the electrodes is of great importance to the optimization of the operating frequency and must be minimized.
Oven controlled crystal oscillators (OCXO) have been widely used in global positioning systems, communications, metering, telemetry control, spectrum, network analyzers and other electronic equipments as a source of time-frequency signal with high precision. Two most important performance indexes of a crystal oscillator are frequency stability and start-up characteristics. In this paper the marriage of hardware and software, practice of dual thermostatic bath and application of optimization technology in temperature control in duel temperature control system enable quicker start and further improve temperature control accuracy and the frequency stability of OCXO. This clever design optimization achieves lower power consumption, higher stability, even more compact size and quicker start.
An all-in-one version of a capacitively coupled contactless conductivity detector is introduced. The absence of moving parts (potentiometers and connectors) makes it compact (6.5 cm(3)) and robust. A local oscillator, working at 1.1 MHz, was optimized to use capillaries of id from 20 to 100 microm. Low noise circuitry and a high-resolution analog-to-digital converter (ADC) (21 bits effective) grant good sensitivities for capillaries and background electrolytes currently used in capillary electrophoresis. The fixed frequency and amplitude of the signal generator is a drawback that is compensated by the steady calibration curves for conductivity. Another advantage is the possibility of determining the inner diameter of a capillary by reading the ADC when air and subsequently water flow through the capillary. The difference of ADC reading may be converted into the inner diameter by a calibration curve. This feature is granted by the 21-bit ADC, which eliminates the necessity of baseline compensation by hardware. In a typical application, the limits of detection based on the 3sigma criterion (without baseline filtering) were 0.6, 0.4, 0.3, 0.5, 0.6, and 0.8 micromol/L for K(+), Ba(2+), Ca(2+), Na(+), Mg(2+), and Li(+), respectively, which is comparable to other high-quality implementations of a capacitively coupled contactless conductivity detector.
Temperature is a key parameter in the description of any physical system. Experimental study of the temperature dependence of conductivity is very valuable in building and testing theoretical models. This fact does not appear to be fully appreciated and exploited in the study of ionic channels of biological membranes owing in part to the lack of an adequate theory for the temperature dependence of conductivity in electrolyte solutions. To redress this imbalance, and to encourage further temperature-dependence studies in ionic channels, we first give explicit expressions for the conductivity of ions in electrolyte solutions in terms of the microscopic parameters of the liquid. We then propose that the dynamics of ion transport in membrane channels are similar to that in bulk electrolyte solutions, except that ions permeating the pore need to surmount a potential barrier, the height of which can be deduced experimentally. Finally, we use our model to analyze the conductance-temperature relationships obtained in two types of single ionic channels.
A new prototype of contactless conductivity detector, smaller and easier to operate than the former version, is described. For a fused-silica capillary with 142-microm wall thickness and voltages up to 25 kV, it can be placed at the low- or high-voltage end of the column. This feature allowed implementation of an apparatus with sample introduction at the grounded end of the column. The input signal is an important parameter for determining the signal-to-noise ratio (S/N) of the detection system. An optimization procedure of its amplitude and frequency is proposed. Although the SIN must be determined by introduction of actual samples, the operating conditions can be optimized merely by changing the signal parameters and by using a mathematical procedure. Thus, an easy and fast optimization routine can be carried out. Mathematical and instrumental backgrounds are discussed, and experimental support of the technique's effectiveness is presented.
A miniaturized capacitively coupled contactless conductivity detector (mini-C(4)D) cell has been designed which is small enough to allow it to slide along the effective capillary length inside the capillary cassette of an Agilent capiillary electrophoresis system (CE) (or other CE brand of similar construction), including the possibility of positioning it close to the point of optical detection (4 cm), or even putting two such detector cells in one cassette. The cell was tested and the performance characteristics (noise, sensitivity, and peak width) were compared with those obtained with the previously used large C(4)D cell. No significant differences were observed. The mini-C(4)D was used in simultaneous separations of common cations and anions where its advantage over a larger C(4)D cell is the ability to vary the point of detection with the mini-C(4)D cell continuously at any point along the capillary length, so that the optimum apparent selectivity can be chosen. Other applications include providing a convenient second point of detection in addition to photometric detection, such as to measure accurately the linear velocity of a zone, or to allow placement of two mini-C(4)D cells in one capillary cassette simultaneously.
A better understanding of the characteristics of the axial contactless conductivity cell could be obtained by carefully studying the effect of the cell geometry on its frequency behavior. A good fit between theoretical and experimental results shows that the axial contactless conductometric detector can effectively be described by the simplest possible equivalent circuitry consisting of a capacitor, resistor, and a second capacitor. The cell constant is largely defined by the length of the gap between the electrodes. The effective electrode size is thus not related to the dimensions of the real electrodes but more closely to the cross-sectional area of the internal diameter of the capillary. Typical experimental values of 20 MOmega and 0.1 pF were obtained for the resistance and capacitances, respectively, of a cell formed by a 2 mm gap between two 4 mm long electrodes fitted with a capillary of 50 microm ID. It could be shown that the diameter of the electrode is not critical and tight coupling of the electrodes to the outer wall of the capillary is not needed. The peak overshoot phenomenon, which has frequently been reported, is an artefact that can be minimized by optimizing the frequency for cell excitation. The frequency setting has to be optimized for each cell design, operational amplifier, electrolyte solution and capillary.
Markets have always influenced the central thrust of the
semiconductor industry. Beginning in the early eighties, the personal
computer (PC) market has been the dominant market influencing the
semiconductor industry. Single-chip microprocessors (MPUs) enabled what
became the huge PC market, which ultimately overshadowed the earlier
minicomputer and mainframe computer markets. The popularity of PCs led
to investments in increasingly more powerful MPUs and memory chips of
ever-growing capacity. MPUs and DRAMs became the semiconductor industry
technology drivers for the data processing needs of the PC. But now,
DSP, as opposed to conventional data processing, has become the major
technology driver for the semiconductor industry as evidenced by its
market growth and the fervour of chip vendors to provide new products
based on DSP technology. The increasing need to digitally process analog
information signals, like audio and video, is causing a major shift in
the semiconductor business. Since DSP is the mathematical manipulation
of those digitized information signals, specialized math circuitry is
required for efficient signal processing-circuitry that was previously
confined to classical DSP chips
The base frequency of oscillators used in the Global System for
Mobile Communication (GSM) network or Global Positioning System (GPS)
receiver applications needs to be very stable with respect to
temperature and supply-voltage variations. One approach to obtain
extremely good frequency stability is the use of oven-stabilized crystal
oscillators. With this kind of oscillator, a frequency stability versus
temperature of a few ppb versus the standard temperature range can be
achieved. In this paper, a digitally compensated crystal oscillator is
described. The system provides a frequency stability of
(Δf)/f<1.5 ppm for a temperature range of -40°C to 90°C
compared to about ±20 ppm for a noncompensated crystal. The core
of the system is an application-specified integrated circuit (ASIC)
fabricated in a standard 0.8-μm CMOS process. The power consumption
for the oscillator running at 13 MHz is 100 mW. The final device
equipped with the ASIC, crystal blank, and a few external components
fits into a 14×9×3 mm3 package
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