Electrokinetic Injection Research Articles

Stereoselective methadone disposition after administration of racemic methadone to anesthetized Shetland ponies assessed by capillary electrophoresis.

The enantioselectivity of the pharmacokinetics of methadone was investigated in anesthetized Shetland ponies after a single intravenous (0.5 mg/kg methadone hydrochloride; n = 6) or constant rate infusion (0.25 mg/kg bolus followed by 0.25 mg/kg/h methadone hydrochloride; n = 3) administration of racemic methadone. Plasma concentrations of l‐methadone and d‐methadone and their major metabolites, l‐ and d‐2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP), respectively, were analyzed by CE with highly sulfated γ‐cyclodextrin as chiral selector and electrokinetic analyte injection from liquid/liquid extracts prepared at alkaline pH. In both trials, the d‐methadone concentrations were lower than those of l‐methadone and the d‐EDDP levels were lower than those of L‐EDDP. For the case of a single intravenous bolus injection, the plasma concentration versus time profile of methadone enantiomers was analyzed with a two‐compartment pharmacokinetic model. l‐methadone showed a slower elimination rate constant, a lower body clearance, and a smaller steady‐state volume of distribution than d‐methadone. d‐methadone and d‐EDDP were eliminated faster than their respective l‐enantiomers. This is the first study that outlines that the disposition of racemic methadone administered to anesthetized equines is enantioselective.

Innovative methods of ground improvement for railway embankment peat fens foundation soil

This paper presents research initiated with the aim of assessing the feasibility of biocementing peat fens soil, a problematic soil underlying many of the embankments of the East Anglia railway network (UK). Biocementation of soil is an emerging, novel, ground improvement technique. It has recently attracted the interest of researchers worldwide because it has been proposed as potentially environmentally superior to chemical grouts and other common soil stabilisers – for example, cement or lime (linked to high carbon dioxide emissions). In this study, the authors screened and isolated non-pathogenic indigenous ureolytic microbial candidates with potential for biocementation from samples originating from peat fens in East Anglia, UK. Four strains were selected as the most suitable candidates, based on their growth rate and their viability in a wide range of temperatures, pH and soil moisture contents corresponding to typical seasonal field conditions. After a number of unconfined compressive strength (UCS) tests, one strain (Bacillus licheniformis) was selected as the most promising for this soil treatment and used for further study. Two different methods of implementation of the treatments were considered: namely, pressure flow soil column and electrokinetic injection. The UCS results supported by calcium carbonate measurements proved that biocementation did occur for both implementation methods and for a number of treatment combinations. Ongoing work on optimisation of treatments and implementation methods is being carried out towards the upscaling of the techniques for in situ implementation, which is planned for the next stage of the research.

A simple and efficient sequential electrokinetic and hydrodynamic injections in micellar electrokinetic chromatography method for quantification of anticancer drug 5-fluorouracil and its metabolite in human plasma.

A simple and sensitive preconcentration strategy using sequential electrokinetic and hydrodynamic injection modes in micellar electrokinetic chromatography with diode array detection was developed and applied for the separation and determination of anticancer agent, 5-fluorouracil and its metabolite, 5-fluoro-2'-deoxyuridine, in human plasma. Sequential injection modes with increased analyte loading capacity using the anionic pseudo-stationary phase facilitated collection of the dispersed neutral and charged analytes into narrow zones and improved sensitivity. Several important parameters affecting sample enrichment performance were evaluated and optimized in this study. Under the optimized experimental conditions, 614- and 643-fold and 782- and 803-fold sensitivity improvement were obtained for 5-fluorouracil and its metabolite when compared with normal hydrodynamic and electrokinetic injection, respectively. The method has good linearity (1-1,000 ng/ml) with acceptable coefficient of determination (r2 > 0.993), low limits of detection (0.11-0.14 ng/ml) and satisfactory analyte relative recovery (97.4-99.7%) with relative standard deviations of 4.6-9.3% (n = 6). Validation results as well as the application to analysis of human plasma samples from cancer patients demonstrate the applicability of the proposed method to clinical studies.

Advances in on-line enzyme assays by sequence analysis-based capillary electrophoresis

Due to unique advantages such as short analysis time, high separation efficiency and sensitivity, easy automation, extremely low sample and reagent volume requirements, and the ability to utilize several detection methods, capillary electrophoresis (CE) is used as a high-efficiency separation technique, and has been developed as a powerful tool for on-line enzyme assays. On-line enzyme assays based on CE have been applied to almost all aspects of enzyme assays over the past two decades, including the evaluation of enzyme activities and kinetics, identification and characterization of enzyme inhibitors and activators, detection of enzyme substrates, investigation of enzyme-mediated metabolic pathways, and proteome analysis. One potential use of enzyme assays is in tracing enzymatic reactions from beginning to the end at high temporal resolution. Measurements of enzyme reactions at high temporal resolution can result in more accurate estimates of reaction mechanisms and reaction rate constants, which is vitally important for improving understanding of the functions of enzymes in metabolism and for identifying the potential use of enzymes in clinical diagnostics. Furthermore, high-throughput online enzyme analysis is of great importance for the analysis of enzyme reactions and enzyme inhibition reactions. The development of accurate, rapid and high-throughput enzyme inhibition screening methods is especially important for accelerating the development of new drugs. Electrophoretically mediated microanalysis (EMMA) and CE-integrated immobilized enzyme microreactor (IMER) are the two most used techniques for online CE enzyme assays. The EMMA technique utilizes different electrophoretic mobilities of enzymes and substrates to initiate reactions within the capillary and to separate the components of the reaction mixture for the final in-capillary quantification. In a CE-integrated IMER, the enzyme is bound to the capillary surface or to a suitable carrier attached to the capillary through physical adsorption, cross-linking, covalent bonding or other methods. The enzyme reactor is usually located at one end of the capillary; the enzyme-catalyzed reaction occurs when the substrates pass through the enzyme reactor and the substrates/products of the enzymatic reaction are separated and online detected by CE at the downstream end of the capillary. In both either techniques, the samples are usually introduced into the capillary by electrokinetic injection or by hydrodynamic injection. Because both injection methods require that the capillary inlet be physically moved from the sample container to the running buffer for CE analysis after each sample injection, it is unlikely that EMMA or microreactor techniques can be successfully used to perform sequential online analysis. Therefore, a CE sequence analysis technique based on rapid sequential injection has been developed as another powerful method for online enzyme analysis. Compared with the widely used electrokinetic and hydrodynamic injection methods used in traditional CE online enzyme analysis methods, rapid sequence injection methods can achieve sequential injection without any physical disturbance of the capillary inlet, allowing for the successful performance of online enzyme assays with high temporal resolution and at high throughput. A rapid, sequential, and automatic sample introduction system is an important part of online enzyme analysis based on CE sequence analysis. Several sequential injection methods such as optical-gating injection, flow-gated injection, two-dimension diffusion injection, flow injection and droplet microfluidics combined with CE have been developed to successfully perform online enzyme assays with high temporal resolution and high throughput. In this paper, we will review recently developed CE online enzyme assays and inhibition studies based on rapid sequential injection. We review the progress and applications of various sequential sample injection approaches that have been developed for sequential on-line CE analysis of enzyme reactions at high temporal resolution and high-throughput screening of enzyme inhibitors, including optical-gating injection, flow gated injection, two-dimension diffusion injection, flow injection and droplet microfluidics.

Offline Selective Extraction Combined with Online Enrichment for Sensitive Analysis of Chondroitin Sulfate by Capillary Electrophoresis

A capillary electrophoresis (CE) method combined with online and offline enrichment for improving the detection sensitivity of chondroitin sulfate (CS) is established. The online enrichment method is based on the field-amplified sample stacking and large volume electrokinetic injection, and offline enrichment is based on the association between cetyltrimethylammonium chloride and CS. Experimental parameters affecting CE method such as the type and pH of background electrolyte, the injection mode and time and the steps of offline enrichment were optimized. Under optimum conditions, the calibration plot between CS concentration and peak area was linear in the range of 1~100μg/mL. The enrichment factor was 130 times and the limit of detection was 50ng/mL. The average recovery was 103.5% and the relative standard deviation of peak area was <2.0%. The method was successfully applied to the quantitative analysis of CS in drugs.

Electrokinetic stacking of particle zones in confined channels enabling their UV absorbance detection on microchips

In this article, we report a simple approach to stacking micro- and nanoparticle zones by electrokinetically migrating them through moderately confined channels of uniform cross-section. Experiments show the reported pre-concentration process to initiate at the tail end of the zone following its electrokinetic injection, with the stacked region migrating faster than the rest of the sample band. This effect causes the particles traveling in front to merge into the stacked region making it grow both in size and concentration. Because the stacked zone also gradually loses particles from its trailing edge, it eventually disintegrates upon running out of particles at its front end. Nevertheless, enhancements in peak height by over 100-fold were recorded using the reported approach for polystyrene beads with diameters comparable to the channel depth. This enhancement however, exhibited a temporal variation as the particle band migrated through the analysis column reaching a maximum value that depended on the particle diameter, particle concentration, channel depth, electric field strength, electroosmotic mobility, etc. Interestingly, the peak area recorded by the detector remained relatively constant during this particle migration period allowing reliable sample quantitation. Moreover, upon incubating antibody-coated particles against an antigen sample, the peak area for the particle zone was seen to scale linearly with the antigen concentration establishing the utility of the reported focusing phenomenon for chemical/biochemical analysis. The noted stacking technique was further applied to enabling UV absorbance detection of particle zones on microchips which then allowed us to determine the colloidal content in actual natural water samples. .

On-line concentration of triazine herbicides in microemulsion electrokinetic chromatography by electrokinetic injection assisted micelle to cyclodextrin stacking.

A fast, simple, environmentally friendly and sensitive on-line concentration method using microemulsion system as background solution (BGS) was developed for the trace detection of propazine, atrazine, simazine in food samples. The electrokinetic injection assisted micelle to cyclodextrin stacking (MCDS) was designed for the enrichment of target compounds. The factors affected enrichment performance, such as the kind of CDs, the amount of CDs, the concentration of methanol in BGS, the concentration of micelle in sample matrix, the concentration of phosphoric acid in BGS and the sample injection time were optimized. The optimized electrophoretic condition was obtained as following: 50 mM α-CD, 20 mM SDS in sample matrix., 80 mM PA and 20% MeOH (v/v) in BGS, sample solution by electrokinetic injection at -10 kV for 80 s. Under the optimized conditions described above, the linear range was 0.1-20 ug/mL with a good linear relationship with a correlation coefficient (r) ≥ 0.9985. The SEFs for the propazine, atrazine, simazine were found to be 123, 85 and 62 respectively. The proposed MCDS-MEEKC method provided an efficient method for trace analysis of triazine herbicides in honey and dendrobium officinale samples.

Field-amplified sample injection combined with CE for the enantiodetermination of cathinones in urine samples.

This work presents a capillary electrophoresis methodology for the enantiodetermination of cathinones in urine employing a liquid-liquid extraction sample pretreatment. The cathinones were enantioseparated by adding a mixture of 8mM 2-hydroxypropyl β-cyclodextrin and 5mM β-cyclodextrin to the background electrolyte, which consists of 70mM of monosodium phosphate aqueous solution at pH 2.5. Field-amplified sample injection was used as preconcentration strategy to improve the sensitivity. We studied various parameters that affect this stacking strategy, in particular, the sample solvent and its pH, the presence or absence of a low conductivity solvent plug introduced before the sample injection, the nature and volume of this plug, and the voltage and time of the electrokinetic injection of the sample. The optimum conditions were achieved by injecting a plug of isopropanol:H2 O 50/50 at 50mbar for 5s prior to the electrokinetic injection of the sample prepared in an aqueous solution of HCl 10-6 M. The sensitivity enhancement factors were from 562 to 601 in terms of peak area and from 444 to 472 in terms of peak height. The method was validated by analyzing spiked urine samples, obtaining a linear range of 25 to 1000ng/mL and limits of detection ranging from 15 to 45ng/mL.

Liquid handling employing a moving drop for electrokinetic sample introduction system for capillary zone electrophoresis

A simple cost-effective moving drop device, with solenoid valves control for programmable liquid handling, was developed for electrokinetic injection in capillary zone electrophoresis (CZE). With a CZE of 50-μm bore fused silica capillary tube and contactless conductivity detector (C4D), mixed anions (Cl−, NO3−, and SO42− as the model) solution was injected at the ground side. Simultaneous quantitative chemical analysis can be achieved. A linear relationship of concentration and the peak height was achieved in the range of 0.5–10 mg L−1 for each anion, with LOD and LOQ being 0.02 mg L−1 and 0.5 mg L−1, respectively. The MVD-CZE system allows continuous operation with a sample throughput of 40 samples/hour. A real sample application was demonstrated for air samples, with one drop (25 μL) collected from a midget bubbler based air sampling unit. The recoveries were found to be 74.4–115.0 %. The developed device was also preliminarily applied for the injection of mixed cations (NH4+, Na+, K+, Ca2+, and Mg2+) at the high voltage side end with optimistic results.

High-Speed Capillary Electrophoresis Using a Thin-Wall Fused-Silica Capillary Combined with Backscatter Interferometry.

High-speed capillary electrophoresis (HSCE) is implemented using a 10 cm total length fused-silica capillary (50 μm i.d., 80 μm o.d.) combined with refractive index (RI) detection using backscatter interferometry (BSI). The short capillary length reduces analysis time while the ultrathin wall (15 μm) efficiently dissipates heat from the separation channel, mitigating the deleterious effects of Joule heating. The separation capillary is mounted on a temperature-controlled heat sink that stabilizes the temperature to ±0.004 °C. This temperature stabilization improves separation efficiency and enhances RI detection. Ohm's Law plots confirm the superior heat dissipation of the HSCE capillary compared to a similarly prepared conventional CE capillary (50 μm i.d., 363 μm o.d.). The speed and efficiency of HSCE combined with universal RI detection is illustrated through the separation of K+, Ba2+, Mg2+, Na+, Li+, and Tris+ in approximately 30 s, with efficiencies greater than 500 000 plates/m. Run-to-run repeatability is explored using nine consecutive electrokinetic injections of a K+, Na+, and Li+ mixture. The average migration times and %RSD for K+, Na+, and Li+ were measured to be 22.04 s (1.59%), 26.81 s (1.38%), and 29.80 s (2.21%), respectively. Finally, we show that the BSI signal is sensitive to the separation voltage through the Kerr mechanism. This leads to peaks in the electropherogram from the injection process that are useful for precisely defining the start of each separation and quantifying the amount of sample injected onto the capillary.

Online preconcentration by electrokinetic supercharging for sensitive determination of berberine and jatrorrhizine in biological samples.

Electrokinetic supercharging, a convenient and powerful online preconcentration technique in capillary electrophoresis, was introduced and evaluated for the determination of two alkaloids, berberine and jatrorrhizine, in mice fecal samples for the first time. The method depended on using a bare fused silica capillary (50 cm × 50 μm i.d.) and applying the voltage of 25 kV with UV detection at 205 nm. Parameters that affect the separation and preconcentration efficiency have been optimized. The optimum conditions used were as follows: background electrolyte consisting of 40mM sodium dihydrogenphosphate containing 30% methanol (v/v); hydrodynamic injection of 20mM KCl (50 mbar × 150 s) as the leading electrolyte; electrokinetic injection of the sample (+15 kV, 120 s) followed by the hydrodynamic injection of 30mM dodecyl trimethyl ammonium chloride (50 mbar × 12 s) as the terminating electrolyte. The results showed that the detection sensitivity of berberine and jatrorrhizine was, respectively, improved up 2740- and 2928-fold compared with normal injection, providing limits of detection lower than 3 ng/mL with good repeatability in areas (relative standard deviation < 3%). In summary, the developed method proved its ability in analyzing trace alkaloids in complicated biological samples.

Analysis of honey using capillary electrophoresis with electrokinetic injection – Direct analysis of viscous samples without sample pretreatment

Although the electrokinetic injection mode is applicable for direct introduction of ionic components from highly viscous samples, this is the first work which studies this special feature of capillary electrophoresis for this purpose. 9 metal cations were determined in honey utilizing direct injection, zone electrophoretic separation and indirect UV detection of the sample components. Reproducibility better than 4 RSD% was found for peak areas and the LOD values ranged between 0.045 and 0.44 mg/kg when injection parameters were set to 7.5 kV × 5 s. In order to remedy the quantitation problems arising from mobility and matrix bias, the applicability of the internal universal calibration was examined. It was found that in cases where the mobilities of cations do not differ from the mobilities of the monitoring ion and the internal universal standard (IUS) by more than 10%, the obtained results agreed well with the data measured with ICP-OES.

Simultaneous enrichment/determination of six sulfonamides in animal husbandry products and environmental waters by pressure-assisted electrokinetic injection coupled with capillary zone electrophoresis

Pressure-assisted electrokinetic injection (PAEKI) as the online method was developed for the simultaneous enrichment of six sulfonamides (SAs), including sulfamethazine (SMZ), sulfamerazine (SMR), sulfamonomethoxine (SMM), sulfadizine (SDZ), sulfamethoxazole (SMX) and sulfacetamide (SFA) in different animal husbandry products and environmental waters samples, followed by capillary zone electrophoresis (CZE) determination. Various parameters affecting the separation performance of CZE and the enrichment efficiency of PAEKI were optimized in detail. Under optimal conditions, the six SAs were completely separated within 8.5 min, and the enrichment factors for SMZ, SMR, SMM, SDZ, SMX and SFA were 39, 47, 53, 50, 54 and 62 folds, respectively, compared with the direct CZE. The limits of detection (LOD) ranged from 0.0018–0.0163 μg/mL, 0.0083–0.0638 μg/mL and 0.0052–0.0478 μg/mL in milk, pork and egg samples, respectively, as well as limits of quantification (LOQ) within 0.0061–0.0503 μg/mL, 0.0253–0.1826 μg/mL and 0.0164–0.1475 μg/mL, respectively. Tap water, lake water and seawater were also examined for investigation of applicability of the proposed method. Satisfactory recoveries in the range of 89–113 % were obtained with the three spiked food samples, and the relative standard deviations were from 1.6 to 7.3%. Simple and effective online enrichment method provides a promising perspective for CZE measurements of SAs in complex matrices with high accuracy, sensitivity and rapidity.

On-Line Electrokinetic Supercharging and Sweeping for the Preconcentration and Determination of Nucleosides and Related Compounds by Capillary Electrophoresis

Nucleosides and related compounds have vital physiological and pharmacological activities. In this study, on-line preconcentration using electrokinetic supercharging (EKS)-sweeping method was proposed to enhance the efficiency of the capillary electrophoresis separation of the nucleosides and related compounds. The separation conditions, including the pH of the borate buffer (terminating electrolyte), the concentration and pH of the phosphate buffer (leading electrolyte), the concentration of sodium dodecyl sulfate (SDS) and the electrokinetic injection (EKI) time, were investigated in detail. The optimum EKS-sweeping conditions were as follows: 40 mM sodium phosphate buffer at pH 2.0 containing 50 mM SDS as the BGE, 120 mM sodium phosphate buffer at pH 2.0 as the leading electrolyte, 30 mM borate buffer at pH 12.0 as the terminating electrolyte, and EKI of the sample at −10 kV for 30 s. The separation was performed by micellar electrokinetic chromatography at −5 kV. Under these conditions, the sensitivity values of five analytes were enhanced from 26 to 109-fold compared to a standard capillary zone electrophoresis (CZE) procedure. The intra- and inter-day repeatability values (as the relative standard deviation) were less than 1.1% and 5.2% for the migration time and lower than 4.4% and 4.8% for the peak areas. Finally, the developed method was successfully applied for the determination of nucleosides and related compounds in Chinese cordyceps samples.

Design and optimization of a fused-silica microfluidic device for separation of trivalent lanthanides by isotachophoresis.

Elemental analysis of rare earth elements is essential in a variety of fields including environmental monitoring and nuclear safeguards; however, current techniques are often labor intensive, time consuming, and/or costly to perform. The difficulty arises in preparing samples, which requires separating the chemically and physically similar lanthanides. However, by transitioning these separations to the microscale, the speed, cost, and simplicity of sample preparation can be drastically improved. Here, all fourteen non-radioactive lanthanides (lanthanum through lutetium minus promethium) are separated by ITP for the first time in a serpentine fused-silica microchannel (70µm wide×70µm tall×33cm long) in <10min at voltages ≤8kV with limits of detection on the order of picomoles. This time includes the 2min electrokinetic injection time at 2kV to load sample into the microchannel. The final leading electrolyte consisted of 10mM ammonium acetate, 7mM α-hydroxyisobutyric acid, 1% polyvinylpyrrolidone, and the final terminating electrolyte consisted of 10mM acetic acid, 7mM α-hydroxyisobutyric acid, and 1% polyvinylpyrrolidone. Electrophoretic electrodes are embedded in the microchip reservoirs so that voltages can be quickly applied and switched during operation. The limits of detection are quantified using a commercial capacitively coupled contactless conductivity detector (C4 D) to calculate ITP zone lengths in combination with ITP theory. Optimization of experimental procedures and reproducibility based on statistical analysis of subsequent experimental results are addressed. Percent error values in band length and conductivity are ≤8.1 and 0.37%, respectively.

Dispersive liquid-liquid microextraction coupled with pressure-assisted electrokinetic injection for simultaneous enrichment of seven phenolic compounds in water samples followed by determination using capillary electrophoresis.

Offline dispersive liquid-liquid microextraction combined with online pressure-assisted electrokinetic injection was developed to simultaneously enrich seven phenolic compounds in water samples, followed by determination using capillary electrophoresis, namely phenol, 4-chlorophenol, pentachlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol, 2-chlorophenol, and 2,6-dichlorophenol. Several parameters affecting separation performance of capillary electrophoresis and the enrichment efficiency of pressure-assisted electrokinetic injection and dispersive liquid-liquid microextraction were systematically investigated. Under the optimal conditions, seven phenolic compounds were completely separated within 14min and good enrichment factors were obtained of 61, 236, 3705, 3288, 920, 86, and 1807 for phenol, 4-chlorophenol, pentachlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol, 2-chlorophenol, and 2,6-dichlorophenol, respectively. Good linearity was attained in the range of 0.1-200μg/L for 2,4-dichlorophenol, 0.5-200μg/L for 4-chlorophenol, pentachlorophenol, 2,4,6-trichlorophenol, 2-chlorophenol, and 2,6-dichlorophenol, as well as 1-200μg/L for phenol, with correlation coefficients (r) over 0.9905. The limits of detection and quantification ranging from 0.03-0.28 and 0.07-0.94μg/L were attained. This two step enrichment method was potentially applicable for the rapid and simultaneous determination of phenolic compounds in water samples.

Highly Sensitive Analysis in Capillary Electrophoresis Using Large-volume Sample Stacking with an Electroosmotic Flow Pump Combined with Field-amplified Sample Injection.

To achieve highly sensitive analysis without labor-intensive experimental procedures in capillary electrophoresis (CE), large-volume sample stacking with an electroosmotic flow pump (LVSEP)-field-amplified sample injection (FASI) was combined with a dynamic coating technique. In this study, poly(vinyl pyrrolidone) (PVP) was employed for the dynamic coating additive. Since a standard fluorescent dye, fluorescein, was well concentrated in a conventional LVSEP, the PVP dynamically-coated capillaries can be also applied to the LVSEP-FASI analysis. In our home-made CE apparatus, however, current breakdown was often caused, especially at a longer electrokinetic injection time due to bubble formation. To avoid the interference of bubble formation, the distance between the tips of the electrode and the capillary in the vertical direction was changed from 0 to 2.5 cm under the magnetic stirring condition. This allowed for a long electrokinetic injection time of up to 20 min, resulting in a sensitive enhancement factor (SEF) of 34900 for fluorescein. The developed method was applied to the chiral analysis of amino acids in CE. As a result, leucine (Leu) was successfully separated in LVSEP-FASI with SEFs of 6420 and 4500 for the D- and L-Leu peaks, respectively.

Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane.

An enantioselective assay for the determination of methadone and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equine plasma based on capillary electrophoresis with highly sulfated γ-cyclodextrin as chiral selector and electrokinetic analyte injection is described. The assay is based on liquid/liquid extraction of the analytes at alkaline pH from 0.1 mL plasma followed by electrokinetic sample injection of the analytes from the extract across a buffer plug without chiral selector. Separation occurs cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ-cyclodextrin. The developed assay is precise (intra- and interday RSD < 4% and < 7%, respectively), is capable to determine enantiomer levels of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in plasma down to 2.5ng/mL, and was successfully applied to monitor enantiomer drug and metabolite levels in plasma of a pony that was anesthetized with racemic ketamine and isoflurane and received a bolus of racemic methadone and a bolus followed by constant rate infusion of racemic methadone. The data suggest that the assay is well suited for pharmacokinetic purposes.

On-line preconcentration of sodium dodecyl sulfate-protein complexes using electrokinetic supercharging method with a prefilled water plug in capillary sieving electrophoresis.

An electrokinetic supercharging (EKS) method with a prefilled water plug at the head column of capillary was developed for on-line preconcentration of sodium dodecyl sulfate (SDS)-protein complexes in capillary sieving electrophoresis (CSE). Conventional EKS is a combination of electrokinetic injection with transient isotachophoresis (tr-ITP). The capillary is first filled with background electrolyte, then an appropriate amount of a leading electrolyte is filled and electro-injection is carried out for certain duration. After that, terminating electrolyte is filled, and tr-ITP is subsequently initiated, followed by capillary electrophoresis (CE) separation. In this work, the performance of EKS was evaluated by integrating multiple sub-methods step by step, and a water plug containing polymer was introduced before electrokinetic injection in order to further improve the concentration effect. The positive effects of the sub-methods were verified, including molecular sieving effect of polymer, field enhanced sample injection (FESI) with and without a water plug, and transient isotachophoretic electrophoresis-based FESI. It was observed that analyte discrimination usually encountered in conventional electrokinetic injection was eliminated due to the similar charge to mass ratios of SDS-protein complexes. Based on these results, a hybrid on-line preconcentration method, EKS with injecting a water plug containing polymer before sample electrokinetic injection, was proposed and used to indiscriminately preconcentrate SDS-protein complexes, which provided a sensitivity enhancement factor of more than 1000. It was very suitable for the analysis of low-abundance proteins, providing the information of their molecular mass.

Pressure-assisted electrokinetic injection stacking for seven typical antibiotics in waters to achieve μg/L level analysis by capillary electrophoresis with UV detection

An effect sensitive CE method for the analysis of four fluoroquinolones (FQs) antibiotics (ofloxacin (OFL), enrofloxacin (ENR), ciprofloxacin (CIP) and norfloxacin (NOR)) and three sulfonamides (SAs) antibiotics (sulfamethazine (SMZ), sulfamethoxazole (SMX) and sulfadiazine (SDI)) in waters was developed by using pressure-assisted electrokinetic injection (PAEKI) stacking technique. The optimal background electrolyte (BGE) was 25.0 mmol/L Na2B4O7, 15.0 mmol/L methyl-β-cyclodextrin (M-β-CD) at pH 10.0 (adjusted by 1.0 mol/L NaOH). The addition of M-β-CD made significant contributions to the separation of OFL, CIP, and NOR, otherwise they co-migrated due to the similar electrophoretic mobilities in the borate buffer. To avoid a cumbersome optimization process of PAEKI, we built a simple method to determine the balance conditions. Herein, the applied voltage and external pressure values to immobilize the bulk flow of BGE could be clearly read from two curves of the BGE velocity respectively induced by pressure and electroosmotic flow (EOF). Under the selected injection condition during PAEKI (0.2 psi vs. −5.2 kV), the sample injection time could sustain 3.0 min without compromising separation efficiency. The sensitivity was improved to 75–110 times in comparison with normal hydrodynamic injection (HDI) mode. The obtained LODs (S/N = 3) of seven antibiotics were in the range of 1.96–4.06 μg/L at UV detection (272 nm), which approached the level of the antibiotics analyzed by CE with fluorescence detection. The precision was characterized by the RSDs of migration times and peak areas, which were averaged at 0.84% and 5.8% for the proposed PAEKI method. Finally, the recoveries of PAEKI were investigated at 83.3–98.7% by spiking FQs and SAs in the actual lake water of Donghua campus to illuminate its feasibility.