A method is described for the colorimetric determination of chromate [chromium(VI)]. It is based on the use of graphene oxide (GO) nanoparticles acting as a peroxidase mimic. A blue color is generated by oxidation of 3,3,5,5-tetramethylbenzidine by H2O2 which is catalyzed by GO. This color-forming reaction is prevented in the presence of 8-hydroxyquinoline (8-HQ). However, in the presence of Cr(VI), the blue color will be formed from TMB owing to the oxidation of the inhibitor 8-HQ by Cr(VI). The color can be measured by a spectrophotometry (at 652 nm) or detected visually. Under optimal experimental conditions, response is linear in the 50 to 430 nM range of chromate concentration, and the limit of detection is 5.8 nM (at S/N = 3). The assay is highly selective and was successfully applied to the determination of Cr(VI) in spiked water samples. Graphical abstract Schematic of the colorimetric assay for Cr(VI). TMB: 3,3,5,5-tetramethylbenzidine.
Keywords: Carbon nanomaterial; Chelate; Chromate; Colorimetric assay; Graphene oxide.