Voltammetric Chloride Sensing Based on Trace-Level Mercury Impregnation into Amine-Functionalized Carbon Nanoparticle Films

A voltammetric sensor for the determination of chloride ions is proposed. At trace level, Hg(II) ions (ca. 15 × 10-12 mol or only approximately 3 Hg²⁺ cations per carbon nanoparticle) are adsorbed at the surface of amine-functionalized carbon nanoparticles in a film supported on a glassy carbon electrode. With this redox-active film, voltammetric chloride determination is possible without loss of mercury/signal in repeatable measurements and over a very wide chloride concentration range. The sensor mechanism is based on the shift of the voltammetric peak potential for the Hg/Hg₂Cl₂ redox transformation in the presence of chloride anions. Only trace-level mercury is employed, so that problems associated with traditional bulk mercury electrodes are not encountered. Differential pulse voltammograms were recorded over a wide range of chloride concentrations resulting in two regimes (from 5 ×10-5 to 1 M and from 1 to 3 M) with linear peak potential shift with a chloride concentration of -63.2 ± 0.09 mV/pCl and -109.1 ± 0.4 mV/pCl, respectively (at 25 °C). The sensor performance is promising in real samples, such as lake water, sea water, and table salt.