Fostering and Understanding Iron Detection at the Ultratrace Level by Adsorptive Stripping Voltammetry with Catalytic Enhancement

Iron detection at the ultratrace level in seawater is at the forefront in chemical oceanography research and analytical methodologies for its determination are actively sought. Voltammetric methods and specifically cathodic stripping voltammetry (CSV) with catalytic enhancement, are particularly fit for this purpose as they avoid any separation and pretreatment step, showing high sensitivity and robustness towards the saline matrix. Here we introduce a simplification in the instrumentation for iron detection by CSV using 2,3-dihydroxynaphthalene (DHN) as the ligand, atmospheric oxygen as the catalytic enhancer and a small 0.5mL cell. The simplification involves the use of a standard, non-specialized voltammetric cup as a holder for the small cell and the introduction of a simple silver wire as a pseudoreference electrode. The latter reduces the risk of sample contamination and is perfectly suited for employment with the small, 0.5mL volume cell. Extensive optimization was performed in both ultrapure and seawater: a square wave frequency of 10Hz was adopted, whereas the ligand concentration did not significantly influence the limit of detection (around 10 and 40pM for ultrapure and seawater, respectively). The latter difference in signal to noise ratio was explained by the kinetics of iron complex reduction. The method was successfully validated by the analysis of a seawater sample with consensus value.