LAUSR

A voltammetric sensor for the determination of chloride ions is proposed. At trace level, Hg(II) ions (ca. $15 \times 10^{-12}$ 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 $5 \times 10^{-5}$ 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.