Efficient and green esterification approach for determining of sodium alkylbenzene sulfonates in dry extracts

Abstract

Linear alkylbenzenesulfonate is an anionic surfactant widely used in detergents and cleaners, both in industrial and household applications as well as a component of pesticides and fertilizers. In this work, the universal effective green approach for sodium alkylbenzenesulfonate esterification to determine these substances in a form of their volatile derivatives by gas chromatography coupled with electron ionization mass-spectrometry (GC–MS) is presented. The approach provides a simple conversion of sodium alkylbenzene sulfonates to a form of alkylbenzenesulfonic acid methyl esters in 98% yield for 20 min at 24 °C. The yield was estimated using high performance liquid chromatography-ultraviolet detection. Trimethyl orthoformate (125 µl) was used as low toxicity alkylation reagent. The obtained volatile derivatives might be redissolved in n-hexane and analyzed by GC–MS in selective ion monitoring mode. The limit of quantification of 20 alkylbenzenesulfonate isomer sum was estimated as 25 ng μL–1 of the analyzed extract. The approach might be applied to food, environmental and biological objects contaminated with alkylbenzene sulfonates. The applicability of the method is shown using dry solvent-free extracts of snow, river sediments, freshwater branching sponge Lubomirskia baikalensis, the whole blood, and widely cultivated plants such as spinach Spinacia oleracea and cucumber Cucumis sativus. The presence of sodium alkylbenzene sulfonates in snow (31.1 ± 1.0 µg L–1) and sediments (208±7 µg g–1 of d.w.) of the world's deepest Lake Baikal tributaries as well as in freshwater sponge (33.6 ± 1.1 µg g–1 of d.w.) was found. The repeatability of measurement is characterized by RSD = 2.24%.