Validation of a Procedure for Determining Priority Phthalates by Gas Chromatography–Mass Spectrometry at a Trace Level of Concentrations in Surface Water with a Background Pollution Level

A procedure for determining trace concentrations of priority phthalates in surface waters with a background pollution level is validated. Lake Baikal, characterized by a minimal concentration of suspended organic matter, a low degree of mineralization, and a background level of concentrations of organic pollutants, is chosen as a natural model for the study. Four priority phthalates are found in Lake Baikal water: dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, and di-(2-ethylhexyl) phthalate present in a range of concentrations of 0.01 to 0.66 μg/L. The procedure for the determination of phthalates includes a single liquid–liquid extraction of phthalates (V_sample = 1 L) and a direct analysis of the extracts by gas chromatography–mass spectrometry. Considering the minimum concentration of suspended particles in the water and high sensitivity of mass spectrometry, stages of filtration of samples and concentration of extracts are excluded from the procedure. Deuterated phthalates are used as surrogate internal standards. The laboratory background of phthalates is assessed by conducting a control experiment and multiple extractions. The limits of determination of phthalates are assessed (0.01–0.17 μg/L); the error of determination is 12 to 38%. The procedure was validated during the monitoring of persistent organic substances in the Baikal water for the period of 2015–2023.