A highly sensitive colorimetric assessment of hexavalent chromium using a digital camera

Simple, low-cost, and sensitive methods for the assessment of hexavalent chromium as an important environmental pollutant are highly desirable, especially under resource-limited settings. Therefore, herein we propose an original approach for the simple, low-cost, selective, and extremely sensitive assessment of Cr(VI) utilizing its catalysis of the micellar sensitized o-dianisidine (DA)-hydrogen peroxide reaction. The initial rate of the amended reaction is monitored by tracing the oxidation product, either by a digital camera video recording or spectrophotometrically at 440 nm, for 120 s from mixing the reactants. The optimized reaction conditions were 5 mmol L^-1 DA, 0.6 mol L^-1 H₂O₂, 2.0 v/v% Tween 20, and 10 mmol L^-1 chloroacetate buffer (pH 4.5 ± 0.1), at 30 °C. The linear calibration graph extends to 90.0 ng mL^-1 Cr(VI) with detection limits (3S_b) of 0.8 and 1.0 ng mL^-1, for the video recording and spectrophotometric procedures, respectively. The amended method was successfully applied to the assessment of Cr(IV) in natural and polluted industrial wastewaters. The analytical data were in excellent statistical harmony with those of the standard ETAAS method. The proposed method is two orders of magnitude more sensitive than the diphenylcarbazide standard spectrophotometric method.Graphical abstract.