Automatic chemical current determination in coulometric stripping potentiometry facilitating calibration‐free trace metal determinations

Abstract

The theory of an improved coulometric stripping potentiometry method, involving automatic determination of the chemical current for each sample, and thus suitable for calibration‐free determination of trace elements in microliter samples is described. The method has been applied to the determination of Zn^II, Cd^II, Pb^II, Tl^I, Cu^II and Bi^III by reductive in situ amalgamation and of As^V, Sn^IV and Cu^II by reductive in situ dissolution on a gold film followed by three consecutive constant current stripping potentiometry measurements permitting the determination of the chemical current. Quantitative reduction (≥99%) of the analyte ions was obtained after four minutes of vibrationally enhanced reductive electrolysis of the 12μL samples placed on top of an inverted glassy carbon disk electrode combined with Ag and Ag/ AgCl counter and reference electrodes. The concentration detection limits ranged from 11 nM for elements oxidized to the monovalent state to 3 nM for elements oxidized to the trivalent state. The mass detection limits ranged from 4.5 pg for Zn^II to 28pg for Tl^I.