Hsueh-Hui Yang

Determination of codeine in urine and drug formulations using a clay-modified screen-printed carbon electrode.

Both flow-injection analysis and square-wave stripping voltammetry were evaluated for the determination of codeine in pharmaceutical formulations using a nontronite clay-modified screen-printed carbon electrode. Compared with a bare screen-printed carbon electrode, the nontronite clay-modified screen-printed carbon electrode exhibited a marked enhancement of the current response of codeine. A linear calibration plot was obtained over the 2.5-45 microM range (correlation coefficient=0.999) in pH 6.0 phosphate buffer solution with a detection limit of 20 nM (S/N=3) by square-wave voltammetry (SWV). While, in flow-injection analysis, the linearity was over 5-120 ng range with a detection limit of 1 ng in 20 microl loop. The nontronite clay-modified screen-printed carbon electrode can be either disposable or reused since the renewal gave a good reproducible surface. Quantitative analysis was performed by the standard addition method for codeine content in both urine and commercially available drugs.

Preconcentration and Electroanalysis of Copper(II) in Ammoniacal Medium on Nontronite/Cellulose Acetate Modified Electrodes

Nontronite/cellulose acetate-coated glassy carbon electrodes (NCA/GCEs) were evaluated for the preconcentration and electroanalysis of Cu2+ in ammoniacal medium by square-wave voltammetry. The NCA/GCEs exhibit good accumulation ability for the [Cu(NH3)4]2+ complex ion via the ion-exchange ability of nontronite. A permselective membrane, cellulose acetate, was applied to strengthen the mechanical stability of the nontronite coating on GCE and to prevent the interference from surface-active compounds. The experimental parameters were studied in detail. The NCA/GCEs show good reproducibility with a relative standard deviation of 2.83% for 15 successive determination of 20 ppb Cu2+. Under optimized conditions, a linear calibration plot was obtained up to 4 ppm Cu2+ with a detection limit (S/N=3) of 1.73 ppb after a preconcentration time of 2 minutes in pH 10 ammonia solution. The practical utility of the NCA/GCEs was illustrated by the measurement of Cu2+ in tap water, groundwater, and pond water.