Sensitive analysis of antibiotics via hyphenation of field-amplified sample stacking with reversed-field stacking in microchip micellar electrokinetic chromatography

Comparison of clonidine and cyproheptadine determination in animal-derived foods by sweeping-micellar electrokinetic chromatography and large volume sample stacking-capillary zone electrophoresis

This study establishes a method for rapid detection of clonidine and cyproheptadine in foods of animal origin. In order to obtain the best detection method, capillary zone electrophoresis (CZE), large volume sample stacking (LVSS), and sweeping-micellar electrokinetic capillary chromatography (sweeping-MEKC) were used respectively. The limits of detection (LODs) of clonidine and cyproheptadine by LVSS-CZE were 0.028 μg mL−1 and 0.034 μg mL−1, and those by sweeping-MEKC were 0.023 μg mL−1 and 0.031 μg mL−1, respectively. Compared with the CZE method, the two online pre-concentration technologies have greatly improved the detection sensitivity and achieved good enrichment results. However, compared with the sweeping-MEKC system, the LVSS system consumed a longer time and was greatly affected by the actual sample matrix. The sweeping-MEKC method was proved to be suitable for real sample analysis. Under the best sweeping-MEKC conditions, clonidine and cyproheptadine could be well separated within 8 min and good linear relationships in the range of 0.1–1.0 μg mL−1 (r 2 > 0.99) were obtained. This method was successfully applied to the determination of clonidine and cyproheptadine in animal-derived foods with the recoveries of 82.3%–90.1% and the relative standard deviations (RSDs) less than 3.11%. The sweeping-MEKC method is simple to operate and has great potential in the rapid detection of clonidine and cyproheptadine in animal-derived foods.

Selective detection of cytochrome C by microchip electrophoresis based on an aptamer strategy

The release of cytochrome C (Cyt C) plays an important role in apoptosis. In this study, selective and sensitive detection of Cyt C based on an aptamer strategy coupled with MCE was developed. Following the binding of a specific aptamer to Cyt C, the aptamer exhibited an irregular state, reducing the binding affinity of a fluorescent probe, and thus preventing the aptamer-Cyt C complexes from detection within the MCE. The height of the detection peak of the residual aptamer linearly decreased, and therefore, the difference in peak height of residual aptamer compared to that of the initial aptamer was used to quantify the captured protein concentration. Experimental conditions such as incubation time, pH, temperature, and ionic strength were optimized. A measurement of Cyt C concentration by MCE was achieved within 135 s, with a limit of detection as low as 0.4 nM. The proposed method has high selectivity and good stability for the detection of Cyt C. The experimental results demonstrate that this method is quick, consumes only a small quantity of sample, is highly selectivity and exhibits high sensitivity.

Monitoring of vancomycin in human plasma via portable microchip electrophoresis with contactless conductivity detector and multi-stacking strategy

A portable microchip electrophoresis (MCE) coupled with on-chip contactless conductivity detection (C⁴D) system was evaluated for the determination of vancomycin in human plasma. In order to enhance the detection sensitivity, a new online multi-stacking preconcentration technique based on field-enhanced sample injection (FESI) and micelle-to-solvent stacking (MSS) was developed and implemented in MCE-C⁴D system equipped with a commercially available double T-junction glass chip. The cationic analytes from the two sample reservoirs were injected under FESI conditions and subsequently focused by MSS within the sample-loading channel. The proposed multi-stacking strategy was verified under a fluorescence microscope using Rhodamine 6G as the model analyte and a sensitivity enhancement factor (SEF) of up to 217 was achieved. The developed approach was subsequently implemented in the aqueous-based MCE, coupled to C⁴D in order to monitor the targeted antibiotic (in this case, vancomycin) present in human plasma samples. The multi-stacking and analysis time for vancomycin were 50s and 250s respectively, with SEF of approximately 83 when compared to typical gated injection. The detection limit of the method for vancomycin was 1.2μg/mL, with intraday and interday repeatability RSDs of 2.6% and 4.3%, respectively. Recoveries in spiked human plasma were 99.0%-99.2%.

Recent progress of sample stacking in capillary electrophoresis (2014-2016)

The term "sample stacking" comprises a relatively broad spectrum of techniques that already form an almost inherent part of the methodology of CZE. Their principles are different but the effect is the same: concentration of a diluted analyte into a narrow zone and considerable increase of the method sensitivity. This review brings a survey of papers on electrophoretic sample stacking published approximately since the second quarter of 2014 till the first quarter of 2016. It is organized according to the principles of the stacking methods and includes chapters aimed at the concentration adjustment principle (Kohlrausch stacking), techniques based on pH changes, micellar methods, and other stacking techniques. Not reviewed are papers on transient ITP that are covered by another review in this issue.

Analysis of antibiotics by CE and their use as chiral selectors: An update

The widespread use of antibiotics in medicine and as growth-promoting agents has increased the demand for suitable analytical techniques for their analysis. Analytical methods based on CE or miniaturized CE systems have proved over the years their ability for the analysis of antibiotics. Since our last review (Electrophoresis 2014, 35, 28-49) several new CE methodologies have been reported for antibiotic analysis. This review presents an update of the literature published from June 2013 to June 2015 for the analysis of antibiotics by CE. UV continues being the most used detection system for antibiotics analysis by CE. Strategies to improve sensitivity as the use of sensitive detection systems and the application of preconcentration techniques appear to be the major developments. Furthermore, the use of portable and miniaturized devices for antibiotic analysis is presented in detail. Applications of the developed methodologies to the determination of residues of antibiotics in biological, food, and environmental samples are carefully described. Finally, new developments and applications of antibiotics as chiral selectors in CE are also included.