A disposable amperometric gas sensor for sulphur-containing compounds based on a chemically modified screen printed carbon electrode coated with a hydrogel

A screen-printed carbon electrode (SPCE), modified with the electrocatalyst cobalt phthalocyanine (CoPc), has been investigated as the base transducer for an amperometric gas sensor to detect hydrogen sulphide (H2S), methanethiol (CH3SH) and dimethyldisulphide (DMDS). A hydrogel comprising agarose in phosphate buffer was used to coat the working and counter/reference electrodes. Cyclic voltammetry was employed to investigate the nature of the electrochemical reactions occurring at the gel/electrode interface. It appeared that the thiols were electrocatalytically oxidised giving rise to one anodic peak over the range studied. DMDS was found to undergo electrocatalytic reduction and exhibited one cathodic peak. The effect of increasing analyte concentration was also studied by cyclic voltammetry and it was found that all three compounds gave linear responses down to low vpm (parts per million by volume) levels. Constant potential amperometry was used to evaluate the proposed gas sensors for use with H2S, CH3SH and DMDS; potentials of +0.6, +0.5 and −0.7 V vs. AgCl electrode were employed. It was found that the linear responses could be obtained for up to 18, 24 and 36 vpm for H2S, CH3SH and DMDS respectively.