Stripping Voltammetric Pyrolytic Graphite Polyaniline Sensor For Simultaneous Determination Of Lead And Cadmium

Abstract

To improve sensitivity of a pyrolytic graphite electrode, a polyaniline thin film was coated on electrode substrate, via multipulse cyclic voltammetry electropolymerization to form pyrolytic graphite polyaniline sensor that was used successfully for simultaneous detection and determination of Cd2+ and Pb2+ ions. Various parameters were studied with reference to anodic stripping–square wave voltammetry signals. The experimental results depicted that the environment-friendly sensor had the ability to increase detection signal for Cd2+ and Pb2+ in the prepared solutions by 1.6 and 2.5 times respectively. Plots of peak current against deposition time, deposition potential, step potential, frequency and amplitude for a mixture of lead and cadmium ions showed high peak current for Pb (NO)3 than CdBr2 solution. The highest peak current for the mixture was 49.0μA obtained for Pb(NO)3 solution, while that for CdBr2 solution was 46.3μA at variable deposition time when other factors were held constant. A plot of peak current against frequency while other factors were held constant resulted in maximum peak current 44 μA and 49 μA at frequency of 45Hz for CdBr2 and Pb(NO)3 solution respectively. A similar plot of peak current against amplitude gave a maximum peak current of 195 μA and 180 μA at amplitude of 0.12V for CdBr2 and Pb(NO)3.This amplitude was chosen for optimization of peak current. A plot of peak current against deposition potential gave optimized peak currents of 46.3 μA and 48.8 μA at deposition potential of 0.05V for CdBr2 and Pb(NO)3, respectively. The plot of peak current against step potential gave two peaks at optimized potential of 0.0405. This suggested existence of inter-metallic bond formation between lead and cadmium ions. Competition between lead and cadmium on active sites of modified pyrolytic graphite electrode may also explain the observed peak suppression of cadmium. Lead seemed to outweigh cadmium for active sites because of its larger diffusivity. The calculation for the values of limits of detection (LOD) and limits of quantitation (LOQ) for cadmium bromide were higher than those of lead nitrate solution. The LOQ and LOD value for cadmium bromide solution was 0.908 ppm and 3.03 ppm respectively', while for Pb(NO)3 solution, the calculated values were 0.11ppm and 0.37ppm in the same order