Electrosynthesis of an imidazole derivative and its application as a bifunctional electrocatalyst for simultaneous determination of ascorbic acid, adrenaline, acetaminophen, and tryptophan at a multi-wall carbon nanotubes modified electrode surface.

In this research, the electrosynthesis of 4-(1H-benzo[d]imidazol-2-ylthio)-5-methylbenze-1,2-diol (as an imidazole derivative) is reported. An imidazole derivative multi-wall carbon nanotube modified glassy carbon electrode (IMWCNT-GCE) was constructed and used as an excellent bifunctional electrocatalyst for oxidation of ascorbic acid (AA) and adrenaline (AD). Cyclic voltammetry was used to calculate the surface electron transfer rate constant, k(s), and the electron transfer coefficient, α, for the electron transfer between MWCNT-GCE and the electrodeposited imidazole derivative. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous rate constant, k', for the oxidation of AA and AD at the IMWCNT-GCE surface were estimated. The modified electrode was found quite effective for the simultaneous determination of AA, AD, acetaminophen (AC), and tryptophan (Trp) in a mixture solution. The detection limits of AA and AD were calculated as 0.96 µM and 0.38 µM, respectively. Finally, IMWCNT-GCE was satisfactorily used for the determination of AA, AD, and AC in pharmaceutical samples.

Electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis for the quantification of trimipramine enantiomers.

A sensitive, simple and reproducible method was developed for preconcentration and determination of trimipramine (TPM) enantiomers in biological samples using electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis (CE). During the extraction, TPM enantiomers migrated from a 5 mL sample solution through a thin layer of 2-nitrophenyl octyl ether NPOE immobilized in the pores of a hollow fiber, and into a 20 µL acidic aqueous acceptor phase presented inside the lumen of the fiber. A Box-Behnken design and the response surface methodology (RSM) were used for the optimization of different variables on extraction efficiency. Optimized extraction conditions were: NPOE as supported liquid membrane, inter-electrode distance of 5 mm, stirring rate of 1000 rpm, 51 V potential difference, 34 min as the extraction time, acceptor phase pH 1.0 and donor phase pH 4.5. Then, the extract was analyzed using optimized cyclodextrin (CD)-modified CE method for the separation of TPM enantiomers. Best results were achieved using 100 mM phosphate running buffer (pH 2.0) containing 10 mM α-CD as the chiral selector, applied voltage of 18 kV and 20°C. The range of quantitation for both enantiomers was 20-500 ng/mL. The method was very reproducible so that intra- and interday RSDs (n=6) were <6%. The limits of quantitation and detection for both enantiomers were 20 and 7 ng/mL, respectively. Finally, this method was successfully applied to determine the concentration of TPM enantiomers in plasma and urine samples without any pre-treatment.