Abstract
Humic acid (HA) and fulvic acid (FA) ubiquitous in the environment will interfere with the electrochemical signals of Cd2+ and Pb2+, thereby decreasing the detection accuracy of square-wave anodic stripping voltammetry (SWASV) for Cd2+ and Pb2+ in soil and sediment extracts. However, insight into the mechanism of HA and FA interference is lacking. This study investigated the interference mechanism of HA and FA on Cd2+ and Pb2+ SWASV currents from multiple perspectives and provided methodological guidance for eliminating the HA and FA interference. Our results indicated that the main interfering factor was the complexation of active functional groups in HA and FA, which converted free-state heavy metal (HM) ions into HA- and FA-complexed HMs (HA-HMs and FA-HMs) undetectable by SWASV. More O-containing groups in FA caused its more severe interference on Cd2+ and Pb2+ than HA. After 60 min of ultraviolet (UV) photolysis, the SWASV current recovery rates of Cd2+ and Pb2+ in HA-HMs almost reached 100%, while FA-HMs achieved the same goal after only 24 min of UV photolysis. The photo-degradation behaviors revealed that the mechanism of interference elimination was that UV photolysis destroyed the molecular structure and active groups of HA and FA, thereby releasing free-state Cd2+ and Pb2+ from HA-HMs and FA-HMs. This study also verified the above-obtained conclusions using real samples. The finding of this study is that advanced oxidation processes can eliminate the interference of HA and FA, thereby improving the detection accuracy of Cd2+ and Pb2+ in soil and sediment extracts by SWASV.
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