Glutathione amperometric detection based on a thiol–disulfide exchange reaction

A method based on a thiol–disulfide exchange reaction is proposed for glutathione detection. The method utilises a reaction between glutathione and an excess of the disulfide cystamine which produces an equimolar concentration of the thiol cysteamine. This latter is then detected at Prussian Blue modified screen printed electrodes at an applied potential of 200 mV versus Ag/AgCl. First the cysteamine analytical parameters were optimised, resulting in a detection limit of 10−6 mol l−1 and a linear range up to 10−4 mol l−1. Reproducibility (R.S.D. = 7%, n = 6) and stability (more than 30 measurements with the same electrode) were satisfactory. Then the reaction between the disulfide cystamine and the thiol glutathione was optimised and a pH of 7.4 with a concentration of cystamine of 10−2 mol l−1 was chosen as the best conditions in terms of reaction rate and sensor sensitivity. Glutathione was then measured under the optimised conditions giving a detection limit of 2 × 10−6 mol l−1 and a linear range up to 5 × 10−4 mol l−1. Blood samples were also tested in order to determine the recovery of the method. Recoveries between 92 and 103% were observed for glutathione concentrations in blood ranging from 0.5 to 3 × 10−3 mol l−1.