A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of copper, bismuth and lead is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of copper, lead and bismuth were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 4.0 μM, pH of 9.0, and accumulation potential at -800 mV vs. Ag/AgCl with an accumulation time of 80 s. The peak currents are proportional to the concentration of copper, bismuth and lead over the 0.4 -300, 1 -200 and 1 -100 ng mL -1 ranges with detection limits of 0.4, 0.8 and 0.7 ng mL -1 , respectively. The procedure was applied to the simultaneous determination of copper, bismuth and lead in the tap water and some synthetic samples with satisfactory results.

A highly conductive electrochemical sensor was constructed for the simultaneous electrochemical determination of levodopa and piroxicam by modification of a glassy carbon electrode with a ZnO–Pd/CNT nanocomposite (GCE/ZnO–Pd/CNTs).

Background: Simultaneous analysis of epinephrine and tyrosine as two effective and important biological compounds in human blood and urine samples are very important for the investigation of human health. Objective: In this research, a highly effective voltammetric sensor fabricated for simultaneous analysis of epinephrine and tyrosine. The sensor was fabricated by the modification of glassy carbon electrode with ZnO-Pt/CNTs nanocomposite (ZnO-Pt/CNTs/GCE). The synthesized nanocomposite was characterized by SEM method. The ZnO-Pt/CNTs/GCE showed two separated oxidation signals at potential ~220 mV and 700 mV for epinephrine and tyrosine, respectively. Also, we detected linear dynamic ranges 0.5-250.0 µM and 1.0-220 µM with a limit of detections 0.1 µM and 0.5 µM for the determination of epinephrine and tyrosine, respectively. The ZnO-Pt/CNTs/GCE was used for the determination of epinephrine and tyrosine in blood serum and human urine samples.