Spectrophotometric determination of Cr(VI) in water using N,N-diethyl-p-phenylenediamine (DPD) as the indicator

Abstract

Nowadays, a number of spectrophotometric methods for Cr(VI) determination have been developed. Whereas most of them are sensitive to pH, metallic ions, temperature, etc, which render them out of feasibility and may result in erroneous measurement. Therefore, to overcome these drawbacks, a new spectrophotometric method with rapid detection, high accuracy and strong anti-interference ability was established. This method is based on the oxidative coloration of N,N-diethyl-p-phenylenediamine (DPD) and Cr(VI) to generate pink-colored DPD•+ radicals which showed maximum absorbance at 551 nm. Accordingly, different reaction parameters were optimized, the calibration curves (linear range 0.85–60 µM) were established with a high sensibility of (3.05 ± 0.02) × 104 M−1 cm−1. The LOD and LOQ were determined to be 0.26 µM and 0.85 µM respectively, accompanied with a stoichiometric coefficient of near 1:3 (1:2.78). The DPD method exerted a satisfactory accuracy in natural water samples and a pretty good anti-interference performance towards various common co-existing metallic ions. Moreover, this method was successfully applied in the Cr(VI)-sulfite and Cr(VI)-hydroxylamine systems. Overall, the study highlights the DPD method as a promising approach for the Cr(VI) determination and provides a new perspective for the practices of spectrophotometry.