Colorimetric detection of chromium(VI) using graphene oxide nanoparticles acting as a peroxidase mimetic catalyst and 8-hydroxyquinoline as an inhibitor

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 TMBowing to the oxidation of the inhibitor8-HQ by Cr(VI). The color can be measured by a spectrophotometry (at 652nm) or detected visually. Under optimal experimental conditions, response is linear in the 50 to 430nM range of chromate concentration, and the limit of detection is 5.8nM (at S/N=3). The assay is highly selective and was successfully applied to the determination of Cr(VI) in spiked water samples.