Local electrochemical sample acidification for the detection of Pb2+ traces†

Electrochemical detection of pollutants (e.g. heavy metals) in real samples often requires the adjustment of pH to allow optimal sensitivity. Such sample pretreatment can be challenging for on-site applications as it implies the use of valves, pumps and storage of base or acid solutions. We report here the use of an electrochemical approach for the control of water sample pH. It offers the possibility for local pH adjustment while simultaneously detecting Pb²⁺, whose detection sensitivity is pH dependent. An effective electrochemical method through local electrochemical acidification is performed to detect Pb²⁺ within a desired pH range without the need to add chemical reagents. Local acidification is based on water electrolysis. An anodic potential is applied to an acidifier to rapidly electrogenerate protons. This allows the sample pH to be tailored to the optimal detection condition. Reduction of the Pt oxide layer formed on the acidifier is key to obtain repeatable results in Pb²⁺ detection. On-site sample acidification is combined with anodic stripping voltammetry to reach a detection limit of 6 ppb (30 nM), which is lower than the World Health Organization guideline value for Pb²⁺ level in drinking water.