VUV-H2O2 photolysis as a pretreatment method for improving the SWASV detection accuracies of Cd2+ and Pb2+ in soil extracts

Abstract

The detection accuracy of square-wave anodic stripping voltammetry (SWASV) for Cd2+ and Pb2+ in soil extracts is interfered with by soluble humic acid (HA). The HA interference originated from the complexation between functional groups of HA with heavy metals (HMs) that decreased the SWASV signals of Cd2+ and Pb2+. The advanced oxidation process combination of vacuum ultraviolet (VUV) and H2O2 (VUV-H2O2) was selected as an appropriate pretreatment method to breakdown HA-HM complexes and restore SWASV accuracy. Key parameters, including photolysis time and H2O2 concentration, were systematically optimized to efficiently eliminate HA interference. The results showed that after HA-HMs underwent photolysis for 15 min under 200 mg/L H2O2, the SWASV signals of Cd2+ and Pb2+ were almost restored, and the SWASV detection accuracies of Cd2+ and Pb2+ were approximately on par with those in pure HMs. Then, the degradation behaviors of HA in the VUV-H2O2 photolysis system were investigated. The results showed that the ultraviolet absorbance, dissolved organic carbon content, and fluorescence intensity of HA-HMs gradually decreased with prolonged photolysis, suggesting that the functional groups of HA were degraded and that the complexing ability of HA to HMs was inhibited. More importantly, the SWASV detection accuracy of Cd2+ and Pb2+ in real soil extract solutions was improved by VUV-H2O2 photolysis, verifying its practicality. The findings of this study further promote the application of electrochemical analysis in soil heavy metal detection.