A histogram-based technique for simultaneous colorimetric determination of malachite green and brilliant green using Triton X-100 micelle

Malachite green and brilliant green are two synthetic triphenylmethane dyes with applications in textile and aquaculture industries. They are considered to be environmental contaminants due to their carcinogenic and mutagenic properties. Both of the dyes have the same bluish green color in aqueous solutions.The aim of this study is to develop a colorimetric analysis as a very simple and cost-effective method to determine the residues of malachite green and brilliant green simultaneously in aqueous industrial samples.This method is based on the alterations in RGB color histograms of the dyes in the presence and absence of Triton X-100 micelle. The images of the samples were taken by a digital camera and converted to RGB color system using MATLAB software. Partial least squares regression as a powerful chemometrics tool was used for multivariate calibrations and quantitative measurements. The performance of the proposed method was compared with a simple spectrophotometric method as a reference.Relative errors of prediction for colorimetric and spectrophotometric analysis respectively in micellar media were 6.56% and 4.61% for malachite green, and 6.38% and 5.24% for brilliant green. The shortest linear ranges for colorimetric and spectrophotometric analysis respectively in micellar media were 0.1-10 mg/L and 0.5-5 mg/L for malachite green, and 0.1-15 mg/L and 0.5-6 mg/L for brilliant green. The recovery percentages obtained from the analysis of the dyes in real samples of fish pond water and textile wastewater ranged between 91-107%.The good correlation between the results of the colorimetric analysis and the spectrophotometric analysis indicates the reliability of the proposed colorimetric method. Also, the results of the relative recovery study showed insignificant matrix effect.This study demonstrates the ability of the colorimetric analysis coupled with chemometrics tools for simultaneous determination of the analytes even with nearly identical colors.