Amperometric determination of sodium thiosulphate using boron-doped diamond electrodes applied to flow injection analysis

A boron-doped diamond (BDD) was used for the first time to study the electroanalysis of sodium thiosulphate in phosphate buffer (pH 6.7) using cyclic voltammetry and flow injection analysis (FIA). Glassy carbon (GC) electrode was also used in order to compare the results under identical experimental conditions. Thiosulphate was found to undergo irreversible electrooxidation on both electrodes. Boron-doped diamond showed highly reproducible and stable voltammograms with higher signal to background ratio in a wider pH range whereas on GC electrode, the anodic peak was ill defined. Under optimal conditions, BDD showed a linear response for the thiosulphate in the concentration ranges from 10 μM to 0.5 mM in the cyclic voltammetry with a detection limit of 5 μM (signal to background ratio S/B=3). The dependence of anodic peak current density on the square root of sweep rate was linear indicating the negligible adsorption of the electroactive species on the electrode surface. From the amperometric hydrodynamic voltammograms, a detection potential of 1.2 V versus Ag/AgCl was chosen for the flow injection analysis which showed a reproducible linear dynamic range at the concentrations of 0.5–100 μM of thiosulphate.