Colorimetric quantification of chromium (VI) ions based on oxidoreductase-like activity of Fe3O4

Chromium (VI) is a highly toxic metal ion that is usually emitted to the environment through different activities like metal plating, leather tanning, wood preservatives treatment, pigment production and mining. Therefore, rapid and simple routine method of detection is highly demanding. Here, we develop a simple method based on the oxidoreductase-like activity of Fe3O4 for colorimetric determination of Cr6+. Simple co-precipitation method was employed to produce Fe3O4. The colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) solution can be oxidized to deep blue colored oxTMB in the presence of Fe3O4, and Cr6+ rapidly. On account of this we determine Cr6+ using Fe3O4 as oxidoreductase catalyst. The method avoids utilization of H2O2 which can compromise the repeatability of measurements due to its instability. The method can detect Cr6+ with a wide linear range of concentration and low limit of detection as small as 34.65 nM that enables determination of the minimum allowable concentration of Cr6+ in drinking water. The assay shows excellent selectivity against potentially interfering metal ions and anions. The method has also employed for quantification of Cr6+ in borehole water samples.