Microextraction-colorimetric determination of anionic surfactants in natural and waste waters

Abstract

An eco-friendly, simple, rapid and cheap method for determining anionic surfactants in natural and waste waters by microextraction-colorimetric method has been developed. The essence of the proposed approach consisted in extraction and concentration of analytes in an acidic medium in the form of associates with organic reagents (methylene blue and acridine yellow) by dispersion liquid-liquid microextraction using a mixture of chloroform-acetonitrile as an extracting and dispersing solvent, followed by aggregation of extractant microparticles by centrifugation and subsequent measurements of color characteristics using a smartphone. The values of the basic components of the RGB colorimetric system were used as an analytical signal to calculate the final color: The selection of optimal conditions for microextraction concentration of anionic surfactants from natural waters (the nature of the extracting and dispergating solvents, the volume of the dispergating solvent) was performed for the sodium dodecyl sulfate — methylene blue system. To study the colorimetric characteristics of the prepared extracts, a smartphone «iPhone X» was used as a color-registering device equipped with a specialized software product «RGBer». To minimize the measurement error by fixing the distance to the object under study and lighting conditions, we propose an installation that increases the accuracy and sensitivity of the determination and makes the method more mobile. The total content of the most common components of detergents was determined: sodium dodecyl sulfate, sulfonol, laureth sulfate and disodium laureth-3-sulfosuccinate. The detection limits ranged within 0.01 – 0.02 and 0.05 mg/liter. The range of detectable contents for all analytes was 0.05 – 1.0 mg/liter. For the determined surfactants, the equations of the relationship between the analytical signal and the concentration were obtained. The calibration graphs are linear with coefficients of the approximation reliability ≤0.98. The correctness of the method was tested on samples of natural water using the spike test procedure. The relative standard deviation of the analysis results does not exceed 0.13. The analysis duration is 20 – 30 min.