Organoclay-film modified electrode for the detection of ultra-traces of Hg2+ ions: Approach of one factor at a time by an experimental design

Abstract

Ultra-trace levels of Hg2+ were detected by DPASV at a glassy carbon electrode modified by an amino-functionalized attapulgite as bulk material, in aqueous solutions containing Hg2+ alone and with Cd2+ and Pb2+. XRD, SEM and TGA/DTG analysis were used to characterize the modified clay mineral prior to its use as electrode modifier. The stripping performance of the thin film modified electrode was therefore evaluated and the experimental parameters were optimized. Based on the open circuit accumulation/voltammetric detection sequence, a linear response was obtained in the Hg2+ concentration range from 1 pM to 4 pM (R2 = 0.997), with a detection limit estimated to 0.043 pM (S/N = 3). Afterwards, Hg2+ ions were also detected in a solution containing cadmium and lead recognised as its most interfering species. The experimental parameters were studied by full factorial design analysis at −0.6 V vs Ag/AgCl and 30 s as potential and electrolysis time respectively. The modified electrode showed a linear response from 0.25 nM to 1.5 nM (R2 = 0.996). The detection limit was found as 0.091 nM (S/N = 3). Interference from coexisting ions was successfully investigated, and the modified electrode was found to be highly selective. The proposed method was successfully applied to the analysis of laboratory tap water.