Determination of manganese and zinc in coastal waters by anodic stripping voltammetry with a vibrating gold microwire electrode

Abstract

Environmental contextMetals in the marine environment play a role in biological processes but can also be toxic. An electrochemical method with a simple microwire electrode is presented that facilitates detection of zinc and manganese in coastal waters. The method is very sensitive and will likely lead to the development of an in-situ monitoring apparatus. AbstractA vibrating, gold, microwire electrode (VGME) is used here to detect low nanomolar levels of dissolved Mn by anodic stripping chronopotentiometry (ASC) and sub-nanomolar levels of dissolved Zn by anodic stripping voltammetry (ASV) in seawater. Mn is detected using a deposition potential (Edep) of –1.35 V, and Zn using Edep = –0.9 V, at pH 8. The method is an example of under-potential deposition (UPD), with positive shifts of the metal oxidation potentials of 0.4–0.6 V compared to the mercury electrode. The limits of detection for Mn (1.4 nM) and for Zn (0.3 nM) in seawater with a 300-s plating time, are better than achieved using other non-mercury based electrodes and nearly as good as a mercury film electrode for Zn. The detection of sub-nanomolar Mn is subject to an unusual interference by arsenate, which lowers the sensitivity when the deposition time is extended beyond 300 s. The VGME has advantages related to robustness, stability and ease of use (no polishing, simple regeneration) facilitating on-site and in-situ use. Zn and Mn are readily measured in seawater of natural pH without the need for reagents, facilitating use of this method in a system for in-situ monitoring. The methods are applied here to coastal seawater (Liverpool Bay, Irish Sea) and can be used for freshwaters such as river water.