Speciation of copper in agricultural soils contaminated by lead using screen-printed electrodes and square-wave anodic stripping voltammetry (SPE-SWASV)

Abstract

An analytical strategy, involving carbon screen printed working electrodes (SPEs) modified with mercury combined with square wave anodic stripping voltammetry (SWASV), was optimized for the total and electrolabile copper concentration determination in the presence of lead. The accuracy of the method was checked by analyzing a solution of mineralized certified reference soil, the mineralization step allowing the quantity of metals to be assumed totally in electrolabile form in the solution of mineralized soil. The influence of the calibration modes and potential matrix effects was investigated. Under optimized conditions, the accuracy (i.e. trueness and repeatability) and robustness were verified. For that, the electrolabile copper concentration and the Relative Standard Deviation (RSD) were evaluated according to the change frequency of the SPE and the analyzed solution after each SPE-SWASV measurement in the solution of the mineralized soil. Additionally, analyses were performed by inductively coupled plasma mass spectrometry (ICP-MS) as a confirmation mean. From statistical tests in a 95% confidence interval, a copper recovery of 97% (regarding a certified value) and a RSD of 9% were found for the electrochemical method. Agricultural soils often contain lead in significant concentration, so analyses were also carried out on lead. This verified that there was no interaction between copper and lead on the measurement. Then, the developed method was applied for the first time in an original strategy consisting of the quantification of the total and the electrolabile amounts of copper and lead in agricultural soils in order to estimate the potential hazard brought by their mobilization from the soil. For that, soils were (i) mineralized to obtain the total metal amounts and (ii) leached to reach the electrolabile ones.