Simultaneous determination of weakly ionizable analytes in urine and plasma samples by transient pseudo-isotachophoresis in capillary zone electrophoresis

Electroosmotic flow assisted pseudophase to pseudophase microextraction for stacking in capillary zone electrophoresis

A stacking technique is proposed to improve the poor detection sensitivity of capillary zone electrophoresis (CZE) with UV detection. A long injection (e.g., 12.4 cm plug) of model anionic analytes prepared in a dilute solution of hexadecyltrimethylammonium bromide (CTAB) was enriched 26-34-x (compared to a typical or 2.1 mm sample injection) via the injection of a micellar solution of sodium dodecyl sulfate (SDS) prior to CZE separation. During sample injection, the CTAB formed a stationary pseudophase coating, which trapped the analytes at the inner walls of a fused silica capillary. The SDS micelles then released the CTAB admicelles via the formation of solution CTAB-SDS catanionic micelles during SDS plug injection and voltage application. As the SDS micelles moved through the sample zone, the formation of the catanionic micelles then released and accumulated the analytes at the front of the injected SDS zone. The stacking technique is called electroosmotic flow (EOF) assisted pseudophase to pseudophase microextraction because the EOF was essential for the formation of CTAB-SDS catanionic micelles for microextraction. Also, the CTAB and SDS aggregates are both pseudophases, which were used to retain and release the analytes from the capillary wall, respectively.

Simultaneous Determination of Ciprofloxacin and Ofloxacin in Animal Tissues with the Use of Capillary Electrophoresis with Transient Pseudo-Isotachophoresis

We have developed a precise and accurate method for the determination of ciprofloxacin and ofloxacin in meat tissues. Our method utilizes capillary electrophoresis with a transient pseudo-isotachophoresis mechanism and liquid–liquid extraction during sample preparation. For our experiment, a meat tissue sample was homogenized in pH 7.00 phosphate buffer at a ratio of 1:10 (tissue mass: buffer volume; g/mL). The extraction of each sample was carried out twice for 15 min with 600 µL of a mixture of dichloromethane and acetonitrile at a 2:1 volume ratio. We then conducted the electrophoretic separation at a voltage of 16 kV and a temperature of 25 °C using a background electrolyte of 0.1 mol/L phosphate–borate (pH 8.40). We used the UV detection at 288 nm. The experimentally determined LOQs for ciprofloxacin and ofloxacin were 0.27 ppm (0.8 nmol/g tissue) and 0.11 ppm (0.3 nmol/g tissue), respectively. The calibration curves exhibited linearity over the tested concentration range of 2 to 10 nmol/g tissue for both analytes. The relative standard deviation of the determination did not exceed 15%, and the recovery was in the range of 85–115%. We used the method to analyze various meat tissues for their ciprofloxacin and ofloxacin contents.

Magnetic polyethyleneimine functionalized reduced graphene oxide as a novel magnetic sorbent for the separation of polar non-steroidal anti-inflammatory drugs in waters

A novel magnetic polyethyleneimine modified reduced graphene oxide (Fe₃O₄@PEI-RGO) had been prepared and then was successfully employed to extract three polar non-steroidal anti-inflammatory drugs (NSAIDs) in different water matrices for the first time coupled with high performance liquid chromatography-diode array detector (HPLC-DAD). The magnetic polyethyleneimine (Fe₃O₄@PEI) composite was first synthesized via one-pot hydrothermal approach and then the Fe₃O₄@PEI-RGO composite was fabricated on the basis of a simple self-assemble approach between positive charged Fe₃O₄@PEI and negative charged GO sheets via electrostatic interaction followed by chemical reduction of GO to RGO. The as-prepared Fe₃O₄@PEI-RGO composite was carefully characterized by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), thermal gravimetric analyzer (TGA), vibrating sample magnetometer (VSM) and zeta potential analysis. As a surface modifier of RGO, PEI not just changed the polarity of RGO to some extent but also offered more adsorption sites to polar NSAIDs. Compared with Fe₃O₄@PEI, Fe₃O₄-RGO and Fe₃O₄@PEI-GO, the as-prepared Fe₃O₄@PEI-RGO composite, which combined the advantage of PEI and RGO, showed higher extraction efficiency for polar NSAIDs. In addition, the adsorption mechanism was also studied. The analytical parameters influencing the extraction efficiency were optimized in detail. A satisfactory performance was obtained under the optimal conditions. The calibration lines were linear over the concentration in the range of 1-800 μg L^-1 for all the analytes with determination coefficients (r²) varying from 0.9972 to 0.9986. The limits of detection (LODs) were 0.2 μg L^-1. The recoveries were between 91.20% and 101.13% with relative standard deviations (RSDs) in the range of 1.09-7.34%. Overall, a fast, convenient, sensitive and eco-friendly method was successfully proposed and became a promising approach for the determination of trace polar NSAIDs in complex matrices.

Monitoring Pb in Aqueous Samples by Using Low Density Solvent on Air-Assisted Dispersive Liquid-Liquid Microextraction Coupled with UV-Vis Spectrophotometry

In this study, AA-DLLME combined with UV-Vis spectrophotometry was developed for pre-concentration, microextraction and determination of lead in aqueous samples. Optimization of the independent variables was carried out according to chemometric methods in three steps. According to the screening and optimization study, 86 μL of 1-undecanol (extracting solvent), 12 times syringe pumps, pH 2.0, 0.00% of salt and 0.1% DDTP (chelating agent) were chosen as the optimum independent variables for microextraction and determination of lead. Under the optimized conditions, R = 0.9994, and linearity range was 0.01-100 µg mL^-1. LOD and LOQ were 3.4 and 11.6 ng mL^-1, respectively. The method was applied for analysis of real water samples, such as tap, mineral, river and waste water.

Contemporary sample stacking in analytical electrophoresis

Sample stacking is a term denoting a multifarious class of methods and their names that are used daily in CE for online concentration of diluted samples to enhance separation efficiency and sensitivity of analyses. The essence of these methods is that analytes present at low concentrations in a large injected sample zone are concentrated into a short and sharp zone (stack) in the separation capillary. Then the stacked analytes are separated and detected. Regardless of the diversity of the stacking electromigration methods, one can distinguish four main principles that form the bases of nearly all of them: (i) Kohlrausch adjustment of concentrations, (ii) pH step, (iii) micellar methods, and (iv) transient ITP. This contribution is a continuation of our previous reviews on the topic and brings an overview of papers published during 2010-2012 and relevant to the mentioned principles (except the last one which is covered by another review in this issue).