[show abstract][hide abstract] ABSTRACT: A novel method that combines two concentration techniques, off-line centrifuge microextraction (CME) and on-line sweeping, is used to determine trace steroids in urine by micellar electrokinetic chromatography (MEKC). The CME-sweeping-MEKC is a promising technique, which has a variety of merits such as high sensitivity, rapid operation, minimal cost, and high sample throughput capability. Using CME-sweeping, over a 500-fold increase in sensitivity could be obtained as compared with the normal hydrodynamic injection without sample stacking. The linear range was 0.05-1 μg mL(-1) with the square of the correlation coefficients ranging from 0.9998 to 0.9999. Detection limits (S/N=3) were 5-15 ng mL(-1) using a photodiode array UV detection at a wavelength of 240 nm. The relative standard deviations were between 2.8% and 3.5% (n=5, progesterone as the internal standard). The diode array UV spectrum used can distinguish the analytes from the interference in the complex sample matrix, which is useful in biological and clinical sample analysis.
[show abstract][hide abstract] ABSTRACT: In this work, two allyl-functionalised ionic liquids (ILs), 1-allyl-3-methylimidazolium hexafluorophosphate and 1-allyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide, were used as selective coating materials to prepare chemically bonded ILs-based organic-inorganic hybrid solid phase microextraction fibres. These fibres were prepared with the aid of γ-methacryloxypropyltrimethoxysilane as bridge using sol-gel method and free radical cross-linking technology. The underlying mechanisms of the sol-gel reaction were proposed, and the successful binding of these functional ILs to the sol-gel substrate was confirmed by Fourier transform infrared spectroscopy. These IL-based sol-gel coatings had porous surface structure, high thermal stability, a wide range of pH stability, strong solvent resistance and good coating preparation reproducibility. They also had high selectivity and sensitivity towards strong polar phenolic environmental estrogens (PEEs) and aromatic amines due to the strong electrostatic interactions, hydrogen bonding and π-π interactions provided by the special molecular structure of these imidazolium ILs. Moreover, their characteristics were somewhat different depending on the type of anions in the IL structure. The practical applicability of these IL-based sol-gel coatings was evaluated through the analysis of PEEs in two real water samples. The detection limits were quite low, varying from 0.0030 to 0.1248 μgL(-1). The linearity was very good in the range of 0.1 to 1000 μgL(-1) for most analytes, and the relative standard deviation values were below 6%. The relative recoveries were between 83.1 and 104.1% for lake water and between 89.1 and 97.1% for sewage drainage outlet water.
[show abstract][hide abstract] ABSTRACT: A novel terminal-vinyl liquid crystal crown ether (2-[4-(3-undeceny-1-yloxy)-phenyl]-2-[4'-(4'-carboxybenzo-15-crown-5)-phenyl] propane) (LCCE) was synthesized and used to modify hybrid silica-based monolithic column possessing vinyl ligands for CEC. The monolithic silica matrix containing vinyl functionalities was prepared by in situ co-condensation of tetramethoxysilane and vinyl-trimethoxysilane via sol-gel process and chemically modified with LCCE by free radical polymerization procedure using alpha,alpha'-azobisisobutyronitrile as an initiator. Morphology of the monolithic column was examined by SEM and mercury porosimetry and the successful incorporation of terminal-vinyl LCCE to the vinyl-hybrid monolith was characterized by infrared spectra. Polycyclic aromatic hydrocarbons, benzenediols, carbamate pesticides and steroids, were successfully separated on the column. The separations were dominated hydrogen bonding supplied by crown ether and hydrophobic interaction offered by the liquid crystal. The effect of ACN concentration on separation performance was studied and the result indicated that RP retention mechanism played an important role. Reproducibilities of migration times for the six selected polycyclic aromatic hydrocarbons were reasonable, with relative standard deviation less than 3.50% for five consecutive within-column runs and were 8.38-9.11% for column-to-column measurements of three columns.
[show abstract][hide abstract] ABSTRACT: Supramolecular chemistry is a new branch of sciences, which deals with the specific recognitions between molecules. The host-guest interactions, which exert by supramolecular compounds, can provide a promising prospect for chromatographic separations with high selectivities. Capillary electrochromatography (CEC) is defined as a very promising micro-separation technique with high efficiency and high selectivity in recent years. As the key component of CEC, the stationary phases have been the research focus of CEC development. This paper reviews the recent progress in supramolecular compounds-based stationary phases (cyclodextrin, calixarene, crown ether and macrocyclic polyamine) for CEC since 1998.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 11/2009; 27(6):737-44.
[show abstract][hide abstract] ABSTRACT: A novel enantioselective polymethacrylate-based monolithic column for capillary electrochromatography was prepared by ring-opening reaction of epoxy groups from poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith with a novel beta-cyclodextrin derivative bearing 4-dimethylamino-1,8-naphthalimide functionalities. Conditions for the ring-opening reaction with respect to different reaction parameters were thoroughly optimized to obtain high electroosmotic flow, separation efficiency and enantioselectivity for the analytes. The nonaqueous mobile phase composition regarding acetonitrile-methanol ratio and the concentration of electrolyte were examined to manipulate the hydrophobic inclusion and anion-exchange interaction between the analytes and chiral stationary phase. It was observed that in addition to beta-cyclodextrin cavity, the electrostatic interaction exhibited pronounced influence on the enantioseparation of acidic analytes. Acidic enantiomers (ibuprofen and naproxen) could be separated with separation factor (alpha) values up to 1.08 and a maximum separation efficiency of 86000 plates/m could be achieved.
Journal of Chromatography 01/2009; 1216(6):1000-7. · 4.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: A method based on solid-phase microextraction (SPME) and post-derivatization on the fiber coupled to gas chromatography-mass spectrometry (GC-MS) was developed for the analysis of fatty acids in sputum from patients with pulmonary tuberculosis. The sputum specimens were digested, hydrolyzed, extracted, derivertized, injected and analyzed without cultivation or isolation of the microorganism. Under optimized conditions, the relative standard deviations (RSD, n=5) for all analytes were below 17% and the limits of detection varied from 1.68 (C(24:0)) to 150.4 microg L(-1) (C(12:0)). Good linearity was observed for all the fatty acids studied except for C(12:0) within a wide concentration range of three orders of magnitudes with the correlation coefficients ranging from 0.91 (C(24:0)) to 0.99 (C(14:0)). Fatty acids in sputum specimens from 21 persons were directly analyzed using the proposed method. The results show that in all the sputum specimens from patients, who were clinically diagnosed with tuberculosis (TB), tuberculosis stearic acid (TBSA) was detected, while in all the sputum samples from persons without TB, TBSA was not found. The possibility of using the proposed method to detect mycobacterium tuberculosis (MTB) via the identification of TBSA in sputum was discussed. The comparison with other methods including sputum culture and microscopy of direct smears indicated that the proposed method is fast and sensitive for the analysis of fatty acids in sputum and offers an alternative for the detection of MTB in sputum.
Journal of chromatography. A 01/2009; 1216(9):1450-7. · 4.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: An ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) was introduced as dynamic coating of a silica monolithic column for capillary electrochromatography of phenols and nucleoside monophosphates. The run-to-run and column-to-column repeatability of migration time for six phenols were satisfactory on this column with relative standard deviation values less than 0.90 and 4.31%, respectively. Anodic electroosmotic flow (EOF) was observed, which increased with the increase of [BMIM][BF4] concentration within 120 mM and when [BMIM][BF4] concentration was above 120 mM, EOF leveled off due to the saturation of [BMIM][BF4] on the monolith. Efficient separation of phenols and nucleoside monophosphates on this dynamically coated monolithic column was obtained, compared with a dynamically coated fused-silica column and unmodified silica monolithic column. The retention behavior of uncharged phenols is mainly manipulated by hydrophobic interactions due to the presence of butyl groups, and that of nucleoside monophosphates is governed by the electrostatic attraction mechanism based on the interaction between positively charged [BMIM][BF4] moieties and negatively charged phosphate groups. In addition, silica matrix also contributes to the separation resolution.
[show abstract][hide abstract] ABSTRACT: 1,4,10,13,16-Pentaazatricycloheneicosane-9,17-dione (macrocyclic polyamine)-modified polymer-based monolithic column for CEC was prepared by ring opening reaction of epoxide groups from poly(glycidyl methacrylate-co-ethylene dimethacrylate) (GMA-co-EDMA) monolith with macrocyclic polyamine. Conditions such as reaction time and concentration of macrocyclic polyamine for the modification reaction were optimized to generate substantial EOF and enough chromatographic interactions. Anodic EOF was observed in the pH range of 2.0-8.0 studied due to the protonation of macrcyclic polyamine at the surface of the monolith. Morphology of the monolithic column was examined by SEM and the incorporation of macrocyclic polyamine to the poly(GMA-co-EDMA) monolith was characterized by infrared (IR) spectra. Successful separation of inorganic anions, isomeric benzenediols, and benzoic acid derivatives on the monolithic column was achieved for CEC. In addition to hydrophobic interaction, hydrogen bonding and electrostatic interaction played a significant role in the separation process.
[show abstract][hide abstract] ABSTRACT: A novel calix open-chain crown ether (p-tert-butylcalixarene-1,3-bis(allyloxyethy) ether)-modified, organic-inorganic hybrid silica-based monolithic column possessing vinyl ligands for CEC is described. The monolithic silica matrix containing a vinyl functionality was synthesized by in situ cocondensation of tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) via sol-gel process and chemically modified with calix open-chain crown ether by free radical polymerization procedure using alpha, alpha'-azobisisobutyronitrile (AIBN) as an initiator. Morphology of the monolithic column was examined by SEM and the successful incorporation of calix open-chain crown ether to the vinyl-hybrid monolith was characterized by infrared (IR) spectra. Compared with an unmodified vinyl-hybrid monolithic column, slightly stronger EOF at pH >7.5 was observed for this monolithic column due to the ionization of phenolic hydroxyls on the lower rim of calixarene. VTMS/TMOS ratios in the reaction mixture were varied and 1:4 was found to be optimum to obtain homogeneous monolith with good permeability. The performance of the column was evaluated by nucleotides, beta-blockers, neurotransmitters, and PAHs as test solutes and compared with that of unmodified vinyl-hybrid monolithic column. Greatly improved column performance was obtained due to the host-guest interaction and intermolecular hydrogen bonding provided by the calix open-chain crown ether moiety. The column efficiencies for neurotransmitters and nucleotides are up to 120 000 and 110 000 plates/m, respectively. Migration time and theoretical plate number reproducibilities were reasonable with RSDs less than 1.0 and 1.8% each for within column runs and not more than 7.2 and 8.6% each for column-to-column measurements, using four nucleotides as test solutes.
[show abstract][hide abstract] ABSTRACT: The paper describes the rapid and label-free detection of the white spot syndrome virus (WSSV) using a surface plasmon resonance (SPR) device based on gold films prepared by electroless plating. The plating condition for obtaining films suitable for SPR measurements was optimized. Gold nanoparticles adsorbed on glass slides were characterized by transmission electron microscopy (TEM). Detection of the WSSV was performed through the binding between WSSV in solution and the anti-WSSV single chain variable fragment (scFv antibody) preimmobilized onto the sensor surface. Morphologies of the as-prepared gold films, gold films modified with self-assembled alkanethiol monolayers, and films covered with antibody were examined using an atomic force microscope (AFM). To demonstrate the viability of the method for real sample analysis, WSSV of different concentrations present in a shrimp hemolymph matrix was determined upon optimizing the surface density of the antibody molecules. The SPR device based on the electroless-plated gold films is capable of detecting concentration of WSSV as low as 2.5 ng/mL in 2% shrimp hemolymph, which is one to two orders of magnitude lower than the level measurable by enzyme-linked immunosorbant assays.
Biosensors and Bioelectronics 03/2008; 23(7):1200-7. · 5.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper describes a novel method that applies pressure-assisted field-amplified sample injection with reverse migrating micelles (PA-FASI-RMM) for the online concentration of neutral analytes in MEKC with a low-pH BGE. After injection of a plug of water into the separation capillary, negative voltage and positive pressure were simultaneously applied to initialize PA-FASI-RMM injection. The hydrodynamic flow generated by the positive pressure compensated the reverse EOF in the water plug and allowed the water plug to remain in the capillary during FASI with reverse migrating micelles (FASI-RMM) to obtain a much longer injection time than usual, which improved stacking efficiency greatly. Equations describing this injection mode were introduced and were supported by experimental results. For a 450-s online PA-FASI-RMM injection, three orders of magnitude sample enhancement in terms of peak area could be observed for the steroids and an achievement of detection limits was between 1 and 10 ng/mL.
[show abstract][hide abstract] ABSTRACT: A simple, sensitive, and accurate method for determination of polybrominated diphenyl ethers (PBDEs) in soil has been developed based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). Permethylated-beta-cyclodextrin/hydroxyl-termination silicone oil (PM-beta-CD/OH-TSO) fiber was first prepared by sol-gel technology and employed in SPME procedure. By exploiting the superiorities of sol-gel coating technique and the advantages of the high hydrophobic doughnut-shaped cavity of PM-beta-CD, the novel fiber showed desirable operational stability and extraction ability. After optimization on extraction conditions like water addition, extraction temperature, extraction time, salts effect, and solvents addition, the method was validated in soil samples, achieving good linearity (r>0.999), precision (R.S.D.<10%), accuracy (recovery>78%), and detection limits (S/N=3) raging from 13.0 to 78.3pg/g.
[show abstract][hide abstract] ABSTRACT: This paper investigates the detection of 2,3-dimethyl-2,3-dinitrobutane (DMNB), a marking agent in explosives, by gas chromatography (GC) with electron capture detection using solid-phase microextraction (SPME) as a sample preparation technique. The 25,27-dihydroxy-26,28-oxy (2',7'-dioxo-3',6'-diazaoctyl) oxy-p-tert-butylcalixarene/hydroxy-terminated silicone oil coated fiber was highly sensitive to trap DMNB from ammonium nitrate matrix. The analysis was performed by extracting 2g of explosives for 30s at room temperature and then immediately introducing into the heated GC injector for 1min of thermal desorption. The method showed good linearity in the range from 0.01 to 1.0mug/g. The relative standard deviations for these extractions were <8%. The calculated limit of detection for DMNB (S/N=3) was 4.43x10(-4)mug/g, which illustrates that the proposed systems are suitable for explosive detection at trace level. This is the first report of an SPME-GC system shown to extract marking agent in explosives for subsequent detection in a simple, rapid, sensitive, and inexpensive manner.
[show abstract][hide abstract] ABSTRACT: A novel titania-hydroxy-terminated silicone oil (titania-OH-TSO) sol-gel coating was developed for solid-phase microextraction of polar compounds. In general, titania-based sol-gel reaction is very fast and need to be decelerated by the use of suitable chelating agents. But in the present work, a judiciously designed sol solution ingredients was used to create the titania-OH-TSO coating without the addition of any chelating agent, which simplified the sol-gel procedure. Thanks to the variety of titania's adsorption sites and their acid-base characteristics, aromatic amines, phenols and polycyclic aromatic hydrocarbons were efficiently extracted and preconcentrated from aqueous samples followed by thermal desorption and GC analysis. The newly developed sol-gel hybrid titania coating demonstrated excellent pH stability, and retained its extraction characteristics intact even after continuous rinsing with a 3 M HCl or NaOH solution for 12 h. Furthermore, it could withstand temperatures as high as 320 degrees C. Practical application was demonstrated through the analysis of six aromatic amines in dye process wastewater. A linearity of four orders of magnitude was obtained with correlation coefficient better than 0.9982. The detection limits ranged from 0.22 to 0.84 microg L(-1) and the repeatability of the measurements was <7.0%. The recoveries of these compounds studied in the wastewater were in the ranges 83.6-101.4%, indicating the method accuracy.
[show abstract][hide abstract] ABSTRACT: Although sample stacking has enjoyed some degree of success in electrophoretic separation techniques, there is still a major problem with complex matrix sample as it suffers tremendously from sample matrix effects. A novel method that combines two concentration techniques, centrifuge microextraction (CME) and on-line back-extraction field-amplified sample injection (OLBE-FASI), is used to determine trace ephedrine derivatives in urine and serum by capillary zone electrophoresis. The CME, integrating the sample cleanup and preconcentration into a single step, is a promising sample preparation method for biological samples. The CME technique provided 9-14-fold enrichment within 10 min. The OLBE-FASI eliminated the need to perform solvent exchange and provided a further concentration of the analytes. Using CME coupled with OLBE-FASI, over a 3800-fold increase in sensitivity could be obtained as compared with the normal hydrodynamic injection without sample stacking. For a 1-mL urine sample, the linear range was 5/10-200 ng/mL with the square of the correlation coefficients (r(2)) ranging from 0.9988 to 0.9994. Detection limits were from 0.15 to 0.25 ng/mL using a photodiode array UV detection at wavelength 192 nm. The possibility of this method to determine ephedrine derivatives in 20-muL serum samples was also demonstrated.
[show abstract][hide abstract] ABSTRACT: A novel open-tubular CEC (OT-CEC) column was prepared by immobilized 5,11,17,23-tetra-tert-butyl-25,27-diethoxy-26,28-dihydroxy-calixarene (Calix) on fused-silica capillary column with sol-gel technology. Calix was initially reacted with gamma-glycidoxypropyltrimethoxysilane (KH-560) to form a new sol-gel precursor (calix-KH-560), and then mixed with another precursor, namely tetraethoxysilane (TEOS). After hydrolysis and condensation, a sol-gel matrix was obtained, in which calix was incorporated. Successful calix-modified sol-gel coating was suggested by infrared (IR) spectra and greatly decreased EOF. In comparison with OT columns prepared by the sol-gel method with TEOS and KH-560 only, the calix-modified sol-gel column showed greatly improved separation of isomeric toluidines, nitrophenols, picolines and neurotransmitters with structural similarity. Migration time and theoretical plate number reproducibility were satisfactory with RSDs less than 1 and 6% each for within column runs and not more than 3 and 7% each for column-to-column measurements, using toluidine and nitrophenol isomers as test solutes on this column. High separation efficiencies (96,000-300,000 plates/m) for basic toluidine isomers were obtained. This column was also successfully employed to combine extraction procedure for the determination of dopamine (DA) and norepinephrine (NE) in Portulaca oleracea L. The recoveries of DA and NE were 93.3 and 94.2%, respectively.
[show abstract][hide abstract] ABSTRACT: In this article, a laboratory-made sol-gel derived fiber with butyl methacrylate/hydroxy-terminated silicone oil (BMA/OH-TSO) coating was first used for headspace solid-phase microextraction (HS-SPME) of medium and long chain fatty acids after derivatization and applied to the analysis of fatty acids in lung tissues by coupling to gas chromatography-mass spectrometry (GC-MS). The experimental parameters for derivatization, HS-SPME and desorption were optimized. Fatty acids in cancerous lung tissues from five patients with lung cancer were determined under the optimized conditions. Normal lung tissues from the same five patients were used as controls. This fiber showed higher extraction efficiency for fatty acids after derivatization when compared with commercial polydimethylsiloxane (PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB) fibers due to the three-dimensional network in the coating. The method presented in this paper showed satisfactory precision, accuracy, linearity and limits of detection (LODs). The relative standard deviation values were below 13.3% (n=5) and the recoveries obtained ranged from 76.35% to 107.0%. The results obtained using the SPME method were also compared with those got by using liquid-liquid extraction (LLE) technique. It was found that the sensitivity could be enhanced by the SPME method. The analysis of the cancerous lung tissues and normal controls from five patients with lung cancer indicated that the main components of lung tissue were palmitic acid (C16:0), stearic acid (C18:0) and lignoceric acid (C24:0). A comparison between the levels of the fatty acids in cancerous lung tissues and normal controls from the same a patient with lung cancer shows that most of the saturated fatty acids showed higher levels in cancerous lung tissues, while unsaturated fatty acids showed higher levels in normal controls on the whole.
[show abstract][hide abstract] ABSTRACT: A novel alumina-based hybrid organic-inorganic sol-gel coating was first developed for solid-phase microextraction (SPME) from a highly reactive alkoxide precursor, aluminum sec-butoxide, and a sol-gel-active organic polymer hydroxyl-terminated polydimethylsiloxane (OH-TSO). The underlying mechanism was discussed and confirmed by IR spectra. The porous surface structure of the sol-gel coating was revealed by scanning electron microscopy. A detailed investigation was conducted to evaluate the remarked performance of the newly developed sol-gel alumina-OH-TSO hybrid materials. In stark contrast to the sol-gel silica-based coating, the alumina-based coating demonstrated excellent pH stability. In addition, good thermal resistance and coating preparation reproducibility are also its outstanding performance. As compared to silica-based hybrids material, the ligand exchange ability of alumina makes it structurally superior extraction sorbents for polar compounds, such as fatty acids, phenols, alcohols, aldehydes and amines. Practical applicability of the prepared alumina-OH-TSO fiber was demonstrated through the analysis of volatile alcohols and fatty acids in beer. The recoveries obtained ranged from 85.7 to 104% and the relative standard deviation values for all analytes were below 9%.
Journal of Chromatography 04/2006; 1108(2):149-57. · 4.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper describes a novel method that applies on-line back-extraction field-amplified sample injection (OLBE-FASI) to the extractants by solvent microextraction (SME) in capillary zone electrophoresis (CZE). To our knowledge, it provides the first report that the water-immiscible solvent samples were directly analyzed by CZE. The water-immiscible solvent sample, sealed with a water plug in the sample vial, was used for direct electroinjection. The water plug with a moderate content of organic solvent, low-conductivity, and the presence of a small amount of H+ provided the highest sensitivity for analyzing positively chargeable compounds, such as cocaine and thebaine. The linear range was at least 2 orders of magnitude, with the square of the correlation coefficient (r2) > 0.9999, and a separate calibration over the range 0.016-10 microg/mL showed the linear range to be approaching 3 orders of magnitude. Detection limits were in the range of 2-10 ng/mL. Because the need to perform solvent exchange (from organic to aqueous solution) was eliminated, the OLBE-FASI method could be conveniently coupled with SME. In the present work, SME-OLBE-FASI-CE was validated for quantitative purposes, and applications to human urine were demonstrated.
[show abstract][hide abstract] ABSTRACT: A novel fiber coated with novel sol-gel (5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-diglycidyloxycalixarene/hydroxy-terminated silicone oil; diglycidyloxy-C/OH-TSO) was prepared for use with headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) and electron capture detection (ECD), which was applied in order to determine nine chlorobenzenes in soil matrices. Due to the improved fiber preparation, which increases the percentage of calixarene in the coating, the new calixarene fiber exhibits very high extraction selectivity and sensitivity to chlorine-substituted compounds. Various parameters affecting the extraction efficiency were optimized in order to maximize the sensitivity during the chlorobenzene analysis. Interferences from different soil matrices with different characteristics were investigated, and the amount extracted was strongly influenced by the matrix. Therefore, a standard addition protocol was performed on the real soil samples. The linear ranges of detection for the chlorobenzenes tested covered three orders of magnitude, and correlation coefficients >0.9976 and relative standard deviations (RSD) <8% were observed. The detection limits were found at sub-ng/g of soil levels, which were about an order of magnitude lower than those given by the commercial poly(dimethylsiloxane) (PDMS) coating for most of the compounds. The recoveries ranged from 64 to 109.6% for each analyte in the real kaleyard soil matrix when different concentration levels were determined over the linear range, which confirmed the reliability and feasibility of the HS-SPME/GC-ECD approach using the fiber coated with diglycidyloxy-C/OH-TSO for the ultratrace analysis of chlorobenzenes in complex matrices.
Analytical and Bioanalytical Chemistry 03/2006; 384(6):1428-37. · 3.66 Impact Factor