Hg detection by measuring thiol groups with a highly sensitive screen-printed electrode modified with a nanostructured carbon black film

A sensor based on a screen-printed electrode (SPE) modified with a stable dispersion of commercially available carbon black (CB) N220 was optimised and challenged with several thiol-containing compounds. This probe showed a significantly enhanced electrochemical activity respect to a bare SPE when tested with thiocholine, cysteine, glutathione and cysteamine. When challenged in amperometric batch mode, the response was stable and showed a linear dependence up to 1 × 10⁻⁵ mol l⁻¹ for thiocholine and cysteine. The very high sensitivity towards these thiols (299 mA mol⁻¹ l cm⁻² for thiocholine and 441 mA mol⁻¹ l cm⁻² for cysteine) was then used as the basis for developing an analytical method for mercury ion detection since a non electroactive complex (thiol–Hg) is formed in the presence of the metal. By selecting an appropriate concentration of thiocholine, a concentration of mercury as low as 5 × 10⁻⁹ mol l⁻¹ (1 ppb) was detected. Satisfactory recovery was obtained when the system was tested on drinking water samples.