Differential pulse anodic stripping voltammetric determination of Hg(II) in water using a sodium-exchanged kaolin-modified carbon paste electrode

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Mercury is a highly toxic pollutant that undergoes complex transformations in aquatic environments and may generate volatile species, posing significant risks to human health and ecosystems. Developing low-cost and accessible methods for mercury monitoring is therefore essential. This work aimed to develop a simple and relatively inexpensive sensor for Hg(II) determination in water. A modified carbon paste electrode containing 10% sodium-exchanged kaolin (MO-Na-CPE), prepared by mixing graphite powder and MO-Na clay with paraffin oil, exhibited a higher stripping response than the unmodified carbon paste electrode (CPE). Using differential pulse anodic stripping voltammetry (DPASV), the MO-Na-CPE generated a peak current approximately ninefold higher than that obtained with the CPE under identical conditions. This enhancement was attributed to ion-exchange-assisted preconcentration of Hg(II) at MO-Na sites prior to stripping. Following optimization of the deposition potential, deposition time and pH, a linear response was obtained over the concentration range of 1–12 nM (201–2407 ng L −1 ) with R 2 = 0.997. The detection limit was 0.35 nM (70 ng L −1 ), well below the WHO guideline value for mercury in drinking-water (6000 ng L −1 ; 30 nM). The method was successfully applied to Hg(II)-spiked tap water samples as a representative drinking-water matrix. Future work will focus on applying the MO-Na-CPE/DPASV approach to drinking-water sources in rural and remote areas, particularly in regions potentially affected by artisanal and small-scale gold mining.