On-line sample preconcentration technique based on a dynamic pH junction in CE-amperometric detection for the analysis of biogenic amines in urine.

It is difficult to detect biogenic amines (BAs) in biological fluids because of their very low concentrations. In this paper, we reported an on-line sample preconcentration method in CE-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 BAs 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 BGE zone. Under optimized 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 derivatization process. Therefore, it is self-evident that this approach for the analysis of real biological samples has great potential in the future.

Sensitive analysis of aminoglycoside antibiotics via hyphenation of transient moving substitution boundary with field-enhanced sample injection in capillary electrophoresis.

A novel field-enhanced sample injection coupled with transient moving substitution boundary method in capillary electrophoresis was developed for aminoglycoside antibiotic (AG) analysis using 18-crown-6-tetracarboxylic acid (18C6H4) as a pseudostationary phase. Results indicated that the stacking mechanism of moving substitution boundary relied on the substitution reaction between 18C6H4-bonded AG complexes and Na(+) at the substitution boundary. The stacking mechanism as well as important parameters governing pre-concentration and separation have been investigated in order to obtain maximum resolution and sensitivity. Under optimized conditions, using a sample prepared in a low-conductivity matrix, the limits of detection for streptomycin, neomycin, and kanamycin were 0.62, 5.9 and 8.6 nM (S/N=3), respectively, and the detection sensitivities were improved 940-, 692-, and 415-fold, respectively. The method also gave accurate and reliable results in the analysis of AGs in river water samples.

Sensitive measurement of polyols in urine by capillary zone electrophoresis coupled with amperometric detection using on-column complexation with borate.

Little is known about human polyol metabolism, but recent studies indicate that abnormal polyol concentrations in body fluids are related to several diseases. In this study, a rapid and sensitive method for the determination of seven major polyols in urine including two groups of polyol isomers, C5-polyols (Rib+Arb+Xyl) and C6-polyols (Sor+Gal+Man), was developed using capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of the working electrode potential, pH, running buffer components and concentrations, separation voltage and injection times were investigated. Under the optimised conditions, seven types of polyols could be perfectly separated via the formation of anionic polyol-borate complexes in a borate buffer solution. Highly linear current responses to the polyol concentrations were obtained with good correlation (0.9984

Ultrasensitive detection of bacteria by microchip electrophoresis based on multiple-concentration approaches combining chitosan sweeping, field-amplified sample stacking, and reversed-field stacking.

In this paper we describe an on-chip multiple-concentration method combining chitosan (CS) sweeping, reversed-field stacking, and field-amplified sample stacking for highly efficient detection of bacteria. Escherichia coli was selected as a model bacterium to investigate the efficiency of this multiple-concentration method. CS was the most suitable sweeping agent for microchip electrophoresis, replacing the usually used cetyltrimethylammonium bromide for capillary electrophoresis. The additive taurine had a synergistic effect by enhancing the interaction between CS and the surface of the bacteria, thus improving the analysis sensitivity. All steps of the concentration method and related mechanisms are described and discussed in detail. A concentration enhancement factor of approximately 6000 was obtained using this concentration method under optimal conditions as compared to using no concentration step, and the detection limit of E. coli was 145 CFU/mL. The multiple-concentration methodology was also applied for the quantification of bacteria in surface water, and satisfactory results were achieved. The application of this methodology showed that the concentration enhancement of bacteria clearly conferred advantageous sensitivity, speed, and sample volume compared to established methods.

Microchip electrophoresis of bacteria using lipid-based liquid crystalline nanoparticles.

The aggregation and adhesion of bacterial cells is a serious disadvantage for electrophoretic separations of bacteria. In this study, lipid-based liquid crystalline nanoparticles were used as a pseudostationary phase to minimise the bacterial aggregation and adsorption to the inner walls of microchannels. Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and Lactobacillus rhamnosus were selected as analytes and were separated by microchip electrophoresis (MCE) with laser-induced fluorescence (LIF) detection using 4.5 mM tris(hydroxymethyl) aminomethane (TRIS)-4.5 mM boric acid-0.1 mM ethylenediaminetetraacetate (EDTA) (TBE) containing poly(ethylene oxide) (PEO) and lipid-based nanoparticles as the running buffer. The mechanism of lipid-based nanoparticles affecting bacterial adhesion and aggregation was discussed and supported by zeta potential experiments. Under the optimal conditions, the three species of bacteria were identified with patterned peaks. This proposed MCE method using lipid-based nanoparticles as running buffer additives was also used to analyse a real yogurt sample, and valuable bacterial information was obtained by the electropherograms.

Nonenzymatic glucose sensor based on over-oxidized polypyrrole modified Pd/Si microchannel plate electrode.

A silicon microchannel plate (MCP) array electrode modified with over-oxidized polypyrrole (OPPy) has been fabricated to detect glucose. The morphology and structure of the electrode are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The OPPy modified silicon MCP array electrode exhibits high electrocatalytic activity as well as excellent selectivity to the electrochemical oxidation of glucose. At a potential of +0.08 V, good sensitivity of 0.37 mA mM(-1) cm(-2) and detection limit of 2.06 µM are attained. The linear range is up to 24 mM with a linear correlation coefficient of 0.997. Furthermore, the electrode is highly resistant to interfering substances because the effects of common coexisting substances can be effectively eliminated by the OPPy film and the response in the current to interferences on the electrode surface is almost negligible. This novel electrode has high potential in nonenzymatic detection of glucose.