Colorimetric detection of Cr(VI) in water using tetramethyl benzidine (TMB) as an indicator

Abstract

Hexavalent chromium (CrVI) poses a serious risk to both human and environment health. Hence, a simple, robust, and efficient analytical method must be developed to monitor the presence of Cr(VI) in the environment. The current investigation concentrated on the colorimetric detection of Cr(VI) using TMB as indicator in the presence of H₂O₂. The study found that Cr(VI) reacts with H₂O₂ to generate hydroxyl radicals which oxidize TMB in a concentration dependent manner. Under optimized conditions, the method obtained a good linearity range (0.025-0.5 mg/L, r² = 0.9944) with LOD and LOQ of 0.009 mg/L and 0.029 mg/L, respectively. The technique was further improved by the addition of EDTA in the sample preparation protocol to reduce the false positive result by the presence of ions like Cu²⁺, Fe³⁺, etc. The study recorded improved Cr(VI) recoveries (81.73-111.40 %) at different fortification levels (0.1-0.5 mg/L). Under optimized conditions, the EDTA added method obtained a good linear response (r² = 0.9952) with a detection limit of 0.023 mg/L which is less than the prescribed limits by WHO (0.05 mg/L) and US EPA (0.1 mg/L) for drinking water. The developed analytical method is very simple without use of any nanomaterial and the results with natural water samples show that it has the potential for real-time detection of Cr(VI) in the environment.

Keywords: Chromium (VI); Colorimetric detection; EDTA; Water analysis.