Mercury-Free Determination of Lead in Water by Cloud Point Extraction and Anodic Stripping Voltammetry

The toxicity of metal ions, such as lead (Pb²⁺) and cadmium (Cd²⁺), has been a worldwide issue since the 1970s. For Pb²⁺ specifically, chronic exposure via drinking water can have lasting health effects. While inductively coupled plasma-mass spectrometry (ICP-MS) and atomic absorption spectroscopy (AAS) are the most common instruments used for the detection of Pb²⁺, electrochemical methods like square wave anodic stripping voltammetry (SWASV) have classically shown promise. However, the determination of metals in a real sample matrix typically requires pretreatment and/or extraction of the analyte from the sample itself. Cloud point extraction (CPE) is a sustainable technique that can be used as a solventless substitute for liquid–liquid or solid-phase extraction. While typically coupled to AAS detection, the applicability of CPE to electroanalysis is still not well understood, nor fully optimized. In this work, CPE was used to isolate Pb²⁺ from water samples for analysis by SWASV with a bismuth-coated glassy carbon (Bi-GC) electrode. This is the first report coupling CPE to electroanalytical detection of trace metals in the absence of mercury (Hg). In addition, a back extraction (BE) step was incorporated to recover Pb²⁺ from the surfactant-rich phase, which resulted in a more sensitive and accurate method. High extraction efficiency was achieved and theoretical limits of detection (LOD) of 2.6, 0.81, and 1.7 μgL⁻¹ were obtained with deposition times (t_dep) of 1, 2, and 3 min, respectively. The optimized CPE-SWASV procedure for Pb²⁺ was selective; only manganese (Mn²⁺) was identified as an interferant. Measurements in more complex water samples were also completed. Overall, this innovative CPE-SWASV approach offers a sensitive, cost-effective, and sustainable alternative to Hg-based electrochemical quantification of Pb²⁺.