A chemometric-assisted method for the simultaneous determination of malachite green and crystal violet in water based on absorbance–pH data generated by a homemade pH gradient apparatus

• For pH gradient, a homemade apparatus was designed.
• It is attractive apparatus for a rapid, accurate and low-cost determination.
• The properties of absorbance–pH matrix from the homemade apparatus were analyzed.
• N-PLS/RBL was used to deal with rank deficient.
• Both analytes were simultaneously determined by using N-PLS/RBL.

An attractive method of generating second-order data was developed by a dropping technique to generate pH gradient simultaneously coupled with diode-array spectrophotometer scanning. A homemade apparatus designed for the pH gradient. The method and the homemade apparatus were used to simultaneously determine malachite green (MG) and crystal violet (CV) in water samples. The absorbance–pH second-order data of MG or CV were obtained from the spectra of MG or CV in a series of pH values of HCl–KCl solution. The second-order data of mixtures containing MG and CV that coexisted with interferents were analyzed using multidimensional partial least-squares with residual bilinearization. The method and homemade apparatus were used to simultaneously determine MG and CV in fish farming water samples and in river ones with satisfactory results. The presented method and the homemade apparatus could serve as an alternative tool to handle some analysis problems.

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