Assessing effects of pH, metal ion and natural organic matter on identification and determination of reduced glutathione by cathodic stripping voltammetry

摘要

The effects of pH, metal ions (i.e. Cu2+, Cd2+, Pb2+ and Zn2+) and natural organic matter (i.e. Suwannee River natural organic matter standard [SRNOM]) on determination of thiol (i.e. reduced glutathione [GSH]) by cathodic stripping voltammetry were evaluated. pH was the most critical parameter to influence GSH voltammogram (i.e. peak shape, position and height). In presence of Cu and Cd, secondary peaks were found at [metal]/GSH > 1 due to formation of GSH complexes at pH = 8.0 (Cu and Cd) and 2.5 (Cu only). On the other hand, Pb showed negligible influence on GSH voltammogram at pH 8.0 and 2.5 within [Pb]/[GSH] = 0.01-2.0. Zn significantly reduced GSH peak height at pH 2.5 at [Zn]/[GSH] = 0.01-2.0. SRNOM peak significantly overlapped with GSH peak at pH 8.0 and [SRNOM] > 1 mg L (1) but was clearly separated from the GSH peak at pH 2.5. However, at pH 2.5, the presence of metal ions and/or SRNOM significantly underestimated GSH concentration (recovery = 21-69%), likely due to metal complexation with GSH and/or SRNOM adsorption onto Hg electrode. The effects of metal ions were minimised by the addition of EDTA. The interference induced by SRNOM adsorption was reduced as the [SRNOM] was reduced to 1 mg L-1 and the recovery was improved to 98%.