Fast Scan Cyclic Voltammetry for Real-Time Metal Speciation Analysis

Electrochemistry is a powerful analytical tool that has been widely used to detect trace metals in natural systems. However, studying the speciation of metals during dynamic events, such as storms and floods, is analytically challenging due to the limited temporal resolution of traditional electrochemical techniques. Additionally, most techniques report the total metal concentration (both complexed and free) that does not reflect the toxicity of these metals, which arise mostly from the free state. To overcome these issues, we previously pioneered the use of fast scan cyclic voltammetry (FSCV) to measure free copper (Cu(II)) and lead (Pb(II)) in real-time in laboratory test solutions. In the current work, we describe the application of our technique measuring different metals in various systems. First, we perform a proof-of-principle complexation study between Cu(II) and a model set of ligands to showcase the feasibility of FSCV to provide complexation information in real-time. We then extend this study towards developing an on-site speciation sensor by developing a mathematical relationship between FSCV response, free Cu(II) concentration, and the complexation constant (Kf) of a range of model ligands. Finally, we apply our technique to rapidly characterize metals with high standard reduction potentials such as Ca(II), Al(III), Zn(II), and Mg(II), that are difficult to analyze via traditional electrochemical techniques. Together, our data showcase the power of FSCV to rapidly provide speciation information for a variety of metals that can be used in the development of cheap, eco-friendly, handheld, and portable on-site metal speciation sensors in the near future