In this work, a new purpose-made portable capillary electrophoresis instrument with a contactless conductivity detector was used for the determination of degradation products of nitrogen mustards in different water samples. The capillary was coated with poly(1-vinylpyrrolidone-co-2-dimethylaminoethyl methacrylate) to avoid analyte-wall interactions. The coating procedure was studied to obtain the best repeatability of the migration time of the analytes. Four different coating procedures were compared; flushing the capillary with the co-polymer at 100 psi for 2 min at 60°C provided the best RSD values (<4%). The analytical method was also optimized. The use of 20 mM of MES adjusted to pH 6.0 with His as running buffer allowed a good baseline separation of the three analytes in different water samples without matrix interferences. The method permitted the detection of the three degradation products down to 5 μM. This article is protected by copyright. All rights reserved
Electrophoresis 2013, 34, 1273-1294. DOI: 10.1002/elps.201200494A powerful method to improve the resolution in MEEKC is the use of additives to the background electrolyte. Migration behaviors of analytes can be easily modified by additives, such as carbon nanotubes, ionic liquids, organic solvents and cyclodextrins. These additives can affect the interaction between microemulsions and analytes.
Two flat gold electrodes are placed vis-à-vis with an epoxy spacer layer that is etched out to give a ca. 100 μm deep electrochemically active trench. A water-insoluble oil phase, here the redox system N,N-diethyl-N’N’-didodecyl-phenylenediamine (DDPD) in 4-(3-phenylpropyl)-pyridine (PPP), is immobilised into the trench to allow anion transfer upon oxidation of DDPD(oil) to DDPD+(oil). In “mono-potentiostatic mode” quantitative transfer/expulsion of anions into the trench oil phase occurs. However, in “bi-potentiostatic mode” feedback currents dominated by rapid plate-to-plate diffusion normal to the electrode surfaces are observed. Comparison of “normal” diffusion and “lateral” diffusion shows that the rate of diffusion-migration charge transport across the oil film is anion hydrophobicity dependent. This article is protected by copyright. All rights reserved
A simple analysis of chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) and phenol was accomplished by coupling a pressurized capillary electrochromatography (pCEC) with amperometric detection. Efficient and reproducible separation of these compounds was achieved within 9 min on a capillary monolithic stationary phase bonded with octadecyl ligands and sulfonate groups, where the selectivity and the retention of analytes can be functionally controlled by optimizing experimental variables, including organic modifier content, mobile phase pH, ionic strength, working electrode potential, separation voltage, and supplementary pressure. A mixed-mode retention mechanism consisting of reverse-phase chromatographic partition, electrostatic repulsion and electrophoresis is considered to play roles in the separation. The use of acetonitrile-based media seems effectual in preventing the unfavorable irreversible adsorption on both wall and electrode, and offer higher sensitivity and less electrode fouling in amperometric detection of phenols. The limits of detection were in the range from 0.02 to 0.2 μg mL−1 with a wide linear dynamic range of 5000-fold, while the peak area precision ranged from 3.2% to 7.5%. The feasibility of using this method in real analysis was evaluated by recovery estimates and comparative experiment on spiked tap water samples. Good recoveries of 80–110% were achieved. Additionally, a paired t-test was used to correlate the two methods. This article is protected by copyright. All rights reserved
It is difficult to detect biogenic amines in biological fluids because of their very low concentrations. In this paper, we reported an on-line sample preconcentration method in capillary electrophoresis-amperometric detection (CE-AD) based on a dynamic pH junction, and a concentration enhancement of approximately 100-fold was achieved compared with the classical CE-AD methods in the simultaneous analysis of six biogenic amines in urine (dopamine, epinephrine, norepinephrine, tyramine, tryptamine, and serotonin). The technique is proposed based on the sharp pH change generated at the boundary between an acidic sample and the basic background electrolyte (BGE) zone. Under optimised conditions, all analytes were successfully focused and well-separated within 20 min with high efficiency and sensitivity (LODs at S/N = 3 ranging from 5.34 to 68.3 nM). For the analysis of urine samples by this method, satisfactory recoveries were obtained without a complicated pretreatment step or derivatisation process. Therefore, it is self-evident that this approach for the analysis of real biological samples has great potential in the future. This article is protected by copyright. All rights reserved