New methodological approach for deep penetrating geochemistry and environmental studies, Part 2; field determination of Co(II)/Ni(II) and Pb(II)/Zn(II) of on-site soil extractions by electrochemical stripping techniques

In the framework of deep penetrating geochemistry for mineral exploration, we report a field electroanalytical method using disposable screen-printed working electrodes able to quantify metal pathfinders in partial extracts of soil samples at the nanomolar level on site. Four metal pathfinders (Co, Ni, Pb, Zn) were chosen due to their geological interest and suitability of electrochemical detection. Square Wave Anodic Stripping Voltammetry (SW-ASV) was developed for the simultaneous detection of Pb(II) and Zn(II) providing limits of detection (LODs) of 1.2 nM and 5.3 nM respectively. A linear scan-cathodic stripping voltammetry (LS-CSV) methodology was developed for the joint detection of Co(II) and Ni(II) yielding LODs of 1.8 nM and 3.5 nM respectively. Method validation was carried out on 14 upper B-horizon soil samples during a field survey. Two wet extraction procedures were applied for soil samples - a strong extraction using HNO (sub 3) and a weak extraction with CaCl (sub 2) . Excellent agreement between electroanalytical methods and ICP-MS was found for Pb(II) while a small underestimation was observed for Zn(II). For Co(II) and Ni(II), the LS-CSV measurements in the HNO (sub 3) extractions were impossible due to the change from low pH to pH to 7.15 which induces precipitation of the Fe and Al. For the CaCl (sub 2) extractions, the Co(II)/Ni(II) results obtained by LS-CSV were in excellent agreement with ICP-MS measurements. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7188747