[Show abstract][Hide abstract] ABSTRACT: A new CE method based on velocity gap (VG) theory has been developed for high-resolution chiral separations. In VG, two consecutive electric fields are adopted to drive analytes passing through two capillaries, which are linked together through a joint. The joint is immersed inside another buffer vial which has conductivity communication with the buffer inside the capillary. By adjusting the field strengths onto the two capillaries, it is possible to observe different velocities of an analyte when it passes through those two capillaries and there would be a net velocity change (NVC) for the same analyte. Different analytes may have different NVC which may be specifically meaningful for enantioseparations because enantiomers are usually hard to resolve. By taking advantage of this NVC, it is possible to enhance the resolution of a chiral separation if a proper voltage program is applied. The feasibility of using NVC to enhance chiral separation was demonstrated in the separations of three pairs of enantiomers: terbutaline, chlorpheniramine and promethazine. All separations started with partial separation in a conventional CE and were significantly improved under the same experimental conditions. The results indicated that VG has the potential to be used to improve the resolving power of CE in chiral separations. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: A novel 96-well liquid-liquid microextraction system combined with modern HPLC was developed and used for the simultaneous analysis of 96 biological samples. The system made use of hollow fibers, a 96-well plate, and a plastic base with a center hole and a side hole. One end of the hollow fiber was sealed, while the other end was attached to one of the holes positioned at the center for the plastic base. The needle was inserted into the liquid from inside or outside of the hollow fiber through the center or the side holes, respectively. The system was tested with plasma samples containing three compounds, acidic indomethacin, neutral dexamethasone, and basic propafenone. Some parameters, such as the kind and dimension of hollow fiber, pH and salt concentration of donor phase, the selection of organic solvent for the acceptor phase, and the extraction time were investigated. Under the optimization conditions, the Log D and drug concentration of indomethacin, dexamethasone, and propafenone in plasma and urine samples were analyzed. Then, the methodology was validated. The results demonstrated that ng/mL levels could be exactly and fast analyzed by our system, which was equipped with an auto-injection sampler, making sample analysis more convenient. This article is protected by copyright. All rights reserved.
Journal of Separation Science 02/2014; · 2.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes the development of a novel high-throughput hollow fiber membrane solvent microextraction technique for the simultaneous measurement of the octanol/water distribution coefficient (log D) for organic compounds such as drugs. The method is based on a designed system, which consists of a 96-well plate modified with 96 hollow fiber membrane tubes and a matching lid with 96 center holes and 96 side holes distributing in 96 grids. Each center hole was glued with a sealed on one end hollow fiber membrane tube, which is used to separate the aqueous phase from the octanol phase. A needle, such as microsyringe or automatic sampler, can be directly inserted into the membrane tube to deposit octanol as the accepted phase or take out the mixture of the octanol and the drug. Each side hole is filled with aqueous phase and could freely take in/out solvent as the donor phase from the outside of the hollow fiber membranes. The log D can be calculated by measuring the drug concentration in each phase after extraction equilibrium. After a comprehensive comparison, the polytetrafluoroethylene hollow fiber with the thickness of 210 μm, an extraction time of 300 min, a temperature of 25 °C and atmospheric pressure without stirring are selected for the high throughput measurement. The correlation coefficient of the linear fit of the log D values of five drugs determined by our system to reference values is 0.9954, showed a nice accurate. The −8.9% intra-day and −4.4% inter-day precision of log D for metronidazole indicates a good precision. In addition, the log D values of eight drugs were simultaneously and successfully measured, which indicated that the 96 throughput measure method of log D value was accurate, precise, reliable and useful for high throughput screening.
Journal of Chromatography B. 01/2014; 967:183–189.
[Show abstract][Hide abstract] ABSTRACT: A copolymer of divinylbenzene and N-vinyl pyrrolidone (DVB-NVP) was synthesized for the purpose of solid phase extraction (SPE). Its performance as an SPE resin was evaluated using six model compounds having different polarities. Aqueous samples containing those compounds were applied to SPE cartridges containing the aforementioned copolymer as well as the classic C18 and Oasis HLB for comparison, and the SPE processed samples were analyzed by using high performance liquid chromatography (HPLC) for quantitation. Then, the copolymer DVB-NVP was sulfonated to modify the surface properties. The surface modified materials were used to analyse complex samples. The results showed that DVB-NVP had high recoveries for the six compounds ranging from 95.55% to 101.08% which were better than those of the C18 and were comparable to those of Oasis HLB. In applying to real samples, the recoveries for dimethyl phthalate, diethyl phthalate and dibutyl phthalate in liquor were 102.55%, 102.99% and 102.11%, with the RSDs of 2.11%, 1.69%, 0.79% respectively. Similarly, the recoveries for clonidine and cyproheptadine in pork were 89.23% and 91.42% with the RSDs of 8.21% and 8.86%, respectively.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 09/2013; 31(9):825-30.
[Show abstract][Hide abstract] ABSTRACT: A new pressure-mediated affinity capillary electrophoresis method for the rapid and accurate determination of drug-protein binding constants is described. A special combination of pressure and electrophoresis is used to shorten the electrophoresis and the overall analysis time to only a few minutes. At the same time, the suitability of this method is checked against a traditional fluorescence spectroscopy method. The binding constants of bovine serum albumin and a total of eight drugs with different pK(a) have been evaluated and compared with those determined by the fluorescence spectroscopy method and other methods in literature. The results indicate that the P-ACE method is well suited for the determination of binding constants with weak interaction (K(b) <10(5) M(-1)).
[Show abstract][Hide abstract] ABSTRACT: An effective, rapid and reliable capillary electrophoresis-laser induced fluorescence (CE-LIF) procedure was built to study the characterization of tyrosine kinase (TK), which was a target for drug screening. In this procedure, CE separated the sample of the TK reaction and LIF selectively detected the fluorescence-labeled polypeptide substrate and product. The precise TK activity was quantitated by introducing the transformation ratio of the substrate (T%) to avoid the deviation resulted from the detection sensitivity and the injection amounts in different runs and different capillaries. By measuring the T%, the effects of various reaction conditions were optimized. Meanwhile, the progression of the enzyme reaction was monitored. The K(m) and V(max) were calculated for TK under the optimized experimental conditions. In addition, the inhibition effectiveness of two model inhibitors, Staurosporine and SU6656 were evaluated. The results indicated that the screening platform based on electrophoresis was suitable for TK analysis and laid a foundation for the HTS of TK inhibitors.
Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 01/2011; 879(1):107-12. · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple and fast method of solid phase extraction (SPE) disk for the determination of trace acrylamide was developed. Using this new technique along with high performance liquid chromatography (HPLC) and ultraviolet spectroscopy (UV) detection, the feasibility of SPE disk method for rapid enrichment was demonstrated in the determination of trace acrylamide in 500 mL tap water. Active carbon was chosen as the adsorbent to be incorporated into the SPE disk as it gave the best adsorption efficiency. Experimental parameters including solvent, elution volume, elution rate, breakthrough volume were optimized to give the highest efficiency of extraction. Under proper chromatographic conditions, acrylamide was easily separated from other impurities. A linear relationship between peak area and mass concentration in the range 0.05-0.5 mg/L of acrylamide was established with a correlation coefficient of 0.998. The limit of detection was 20 ng/L. The recoveries for acrylamide with different concentrations and volumes ranged from 94.12% to 100.2%. The relative standard deviations (RSDs) were 2.09%-4.51% (n=3). The recovery for acrylamide spiked into a tap water sample was 79. 96%. The method is simple, fast, sensitive and suitable for the determination of acrylamide in tap water.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 12/2010; 28(12):1196-9.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the results obtained from a novel multifunctional analysis platform established on the basis of wide-bore electrophoresis (WBE) and CE. The WBE–CE system integrated various analytical steps including separation, transfer, reaction, detection, and storage into a single system. During the WBE–CE process, a distinct three-electrode format was adopted to continuously separate and transfer samples between WBE and CE without the interruption of switching on-and-off the power suppliers. This continuous mode of operation also helped to eliminate the need for exactly timing the transfer of specific samples zone from WBE to CE and avoided the danger of missing specific samples. Samples representing mixtures of acids, bases, or proteins were analyzed on this system for evaluating its feasibility and applicability. The results indicated that the resolution achieved on this WBE–CE system was better than either the WBE or the CE alone. Further, samples transferred out of the WBE system could participate in online reaction, such as enzymatic reaction in the CE. Alternatively, samples from the WBE system could be transferred out and stored offline in a vial for post-transfer reaction. The results demonstrated that this WBE–CE system has the potential to be a multifunctional platform for a range of applications.
[Show abstract][Hide abstract] ABSTRACT: A novel amphiphilic silica-based monolithic column having surface-bound octanoyl-aminopropyl moieties was successfully prepared by a one-step in situ derivatization process. As expected, the amphiphilic monolithic column exhibited RP chromatographic behavior toward non-polar solutes (e.g., alkyl benzenes) with high column performance. As the pH of the buffer inside the column increases, the EOF changed from -2.65 x 10(-8) m(2) V(-1) s(-1) at pH 3.0 to 1.20 x 10(-8) m(2) V(-1) s(-1) at pH 8.0 with the reversion of EOF at about pH 6.4. Using acidic mobile phase, five aromatic acids can be efficiently separated in less than 6 min under co-EOF conditions. For basic compounds, symmetrical peaks were obtained due to the existence of hydrophilic acyl amide group, which can effectively minimize the adsorption of the positively charged basic analyte to the silica-based surface of the capillary column.
[Show abstract][Hide abstract] ABSTRACT: A novel, high-performance wide-bore electrophoresis (WE) system with inner-cooling has been developed. By introducing the mode of a shell and tube heat exchanger into this system to remove Joule heat generated during electrophoresis, it is feasible to extend electrophoresis from the conventional capillary (i.d. <100 microm) to a wide-bore tube (i.d. >1000 microm). The wide tube allows the loading of over 1.0 microL of the sample with an LOD of 3.0 x 10(-4) mg/mL (signal-to-noise ratio, 3:1). Satisfactory separations of model compounds have been achieved on the WE system.
[Show abstract][Hide abstract] ABSTRACT: An effective, rapid and economical CE/LIF (capillary electrophoresis/laser-induced fluorescence) method was developed and applied to the characterization of signal peptidase (SPase) enzyme, which is a target for the screening of new drug candidates. In this method, CE separates the product from the substrate and LIF selectively detects the fluorescence-labeled product and substrate. By measuring the increase of the product as a function of time, one can monitor the progression of the enzyme reaction. The progression curves were also used for screening inhibitors for this enzyme. The effects of various reaction conditions were also studied and discussed. In addition, this CE/LIF method was applied to the determination of the enzyme activity, the quality control of the substrate and/or enzymes, and the cross-reactivity of inhibitors to the enzyme. It can be concluded that this method is suitable for high throughput screening (HTS) assays because it can deliver fast, sensitive, quantitative, and reliable results.
[Show abstract][Hide abstract] ABSTRACT: A model mixture of six aromatic acids has been separated using a laboratory-made wide-bore electrophoretic device with aminopropyl-modified nanoparticles used as pseudostationary phase. Optimization of preparation of nanoparticles by an electrospray (ES) method is described. With the optimized electrophoretic method, 30 mmol/L acetate running buffer, pH 4.5, containing 1.0 mg/mL of nanoparticles as an additive was used, and 3.0 kV applied potential, improved resolution was achieved. The average theoretical plate number obtained was above 5.0 x 10(4) theoretical plates per meter with the highest value achieved in certain runs exceeding 1.0 x 10(5) theoretical plates per meter, which was better than previously reported results (approximately 6.7 x 10(4) theoretical plates per meter). Furthermore, repeatabilities of 2, 6.5, and 6% were obtained for the migration time, peak areas, and peak height, respectively. Additionally, sample capacity and sensitivity were improved by hundredfold using the novel wide-bore electrophoresis system compared to traditional CE.
[Show abstract][Hide abstract] ABSTRACT: A new wide-bore electrophoresis (WE) system adopting an inner cooling device was set up to perform electrochromatography. In this system, a quartz tube of 1.2 mm inner diameter was used as the separation channel. The Joule heat generated during electrophoresis was removed timely through the outer surface of the quartz tube and a cooling capillary inserted into the quartz tube. A proper coolant passed through the cooling capillary to further improve the cooling efficiency. In the primary research, a polyacrylamide monolithic column was successfully prepared in this quartz tube. Then it was evaluated in the electrochromatographic mode. An electric field strength as high as 625 V/cm can be applied to this system without obvious deviation of the current from the linear curve of the Ohm plot. Sample volume as high as 1 microL was injected into the WE system and reasonable efficiency was obtained for separation of the test compounds.
[Show abstract][Hide abstract] ABSTRACT: The EOF pump was successfully used as a means of introducing samples into a capillary system. An improved sample injection device has been developed using a Teflontrade mark union (TU) to link the two capillaries together. The capillary applied high voltage served as the EOF pump to pull the liquid inside while the other one served the purposes of isolating the electric field. Using the bias degree (BD) and SD of bias (SDB), it was possible to quantitatively determine the sampling bias and evaluate the effectiveness of injection approaches in bias elimination. Several related factors were evaluated, and it was found that TU approach could fully eliminate the bias under the optimal conditions. The fracture did not affect the efficiency, leak, or dilute the sample significantly. This approach was effective under both normal and reverse EOF situations and adapted to real samples. Finally, a TU method using grounded injection electrode was proposed and shown to be suitable for samples with low conductivity and high injection voltage.
[Show abstract][Hide abstract] ABSTRACT: A general pumping injection (PI), which involves the use of two capillaries with different diameters, was taken to evaluate systematically the effects on eliminating sample bias associated with the electrokinetic injection process in CE. One end of the separation capillary of the smaller diameter was inserted into another pumping capillary of larger diameter. When a high voltage was applied to the pumping capillary, the EOF generated inside will act as a pump to drive the solution stream in the separation capillary. The results have demonstrated that PI is suitable for both normal and reverse EOF situations. Second, the bias degree (BD) and SD of bias we presented were used to evaluate the degree of the bias under different conditions, and the factors of bias elimination have been investigated. Under optimal conditions, the bias was satisfactorily eliminated by PI. This EOF pumping system was successfully applied to the analysis of samples in CEC for a bias-free injection. Moreover, this two-capillary pumping system did not significantly affect the EOF, current, and the column efficiency of the separation process. Finally, a PI with grounded electrode was proposed and shown to be suitable for samples with low conductivity and ions with different mobility.
[Show abstract][Hide abstract] ABSTRACT: A new direct method has been developed to determine protein-drug binding based on hollow fiber membrane solvent microextraction. Hollow-fiber membrane solvent microextraction coupled with high-performance chromatography with UV detection was employed to evaluate the binding characteristics of drugs to bovine serum albumin (BSA) and blood serum. It was found that the BSA and matrix in the blood serum did not interfere with the measurement. The method is simple and fast. It lacks the drawbacks of some conventional analytical techniques, such as taking much long time and requiring large volume sample consumption.
[Show abstract][Hide abstract] ABSTRACT: A silica-based CEC monolithic column with mixed modes of RP and weak anion-exchange (WAX) was successfully prepared by using the sol-gel technique at mild temperature. The synthesizing procedure was optimized by changing the ratios of tetraethoxysilane (TEOS), aminopropyltriethoxysilane (APTES), and octyltriethoxysilane (C(8)-TEOS) in the mixture. While serving as WAX group, the amino group dominated the charge on the surface of the capillary column and generated an EOF from cathode to anode at low pH. At pH above 7.5, a cathodic EOF was observed due to the full ionization of silanol group and the suppression in the ionization of amino group. The morphology of monolithic columns was examined by SEM, and the performance of column was evaluated in detail by separating different kinds of compounds. As expected, the monolithic column exhibited RP chromatographic behavior for neutral solutes. Fast and efficient separation of six aromatic acids was obtained using acidic mobile phase with column efficiency up to 160,000 plates/m. Symmetrical peaks can be obtained for aromatic amines because positively charged amino groups on the surface can effectively minimize the adsorption of positively charged analytes to the stationary phase.
[Show abstract][Hide abstract] ABSTRACT: Multiplexed (96-lane) capillary electrophoresis with laser-induced fluorescence (MCE-LIF) detection was used for the rapid analysis of extracellular signal-regulated protein kinase (ERK) levels from in vitro cell extracts. The levels of ERK enzyme in cell extracts were determined by monitoring the conversion of a fluorescent-labeled peptide substrate to a phosphorylated fluorescent-labeled peptide product using MCE-LIF. The incorporation of a fluorescent internal standard was found to improve the precision of the analysis. The enzyme assay conditions including substrate concentration, reaction time and enzyme linear range were rapidly optimized using the MCE-LIF approach for both direct and immunoprecipitation-based ERK assays. The levels of ERK from in vitro cell extracts stimulated with angiopoietin 1 (Ang1*) were determined using the MCE-LIF approach. The advantages of MCE-LIF for developing and applying enzyme assays, as well as the figures of merit for the direct and immunoprecipitation ERK assays, are discussed.
Journal of Chromatography B 07/2003; 789(2):323-35. · 2.49 Impact Factor