Microextraction–Colorimetric (Fluorimetric) Determination of Cationic and Anionic Surfactants in Food Products

A method is proposed for the determination of cationic and anionic surfactants in food products based on the use of dispersive liquid–liquid microextraction of surfactant ion pairs with organic reagents (eosin and acridine yellow) and measurements of the colorimetric parameters of the fluorescence of extracts using a smartphone. Upon the irradiation of the extracts of ion pairs anionic surfactant–acridine yellow and cationic surfactant–eosin with ultraviolet light (365 nm), green and yellow fluorescence were observed, respectively. The analytical signal (Ar) was the value of the colorimetric parameters in the RGB system: Ar = $$\sqrt {{{{{\text{(}}{{R}_{{\text{0}}}} - {{R}_{x}}{\text{)}}}}^{2}}{\text{ + (}}{{G}_{{\text{0}}}} - {{G}_{x}}{{{\text{)}}}^{2}}{\text{ + (}}{{B}_{{\text{0}}}} - {{B}_{x}}{{{\text{)}}}^{2}}} .$$ Procedures for determining the total amount of surfactants in food products (milk, vegetables and fruits, meat, and drinking water) are developed using an example of cetylpyridinium, myristalconium, benzalkonium, didecyldimethylammonium, alkyldimethyl(ethylbenzyl)ammonium, dodecyl sulfate and sodium alkylbenzenesulfonate chlorides. The limits of detection and quantification are in the ranges 0.005–0.05 and 0.01–0.1 mg/L, respectively. Calibration graphs are linear in the concentration range 0.01–1 mg/L with approximation confidence coefficients ≥0.99. The duration of analysis is 20–30 min; the relative standard deviation of the results of analysis does not exceed 0.24.