Thin-Layer Chromatography of Methylated Derivatives of Linear Alkylbenzene Sulfonates in Water Analysis by Gas Chromatography–Mass Spectrometry

Abstract

Sodium alkylbenzene sulfonates (ABS), or linear alkylbenzene sulfonates (LAS), are among the most common synthetic anionic surfactants and water pollutants, capable of causing both acute and chronic toxic effects on aquatic organisms. The selective determination of sodium alkylbenzene sulfonates as a distinct class of anionic surfactants in complex natural matrices is feasible by gas chromatography with mass spectrometric detection (GC–MS) in the form of linear alkylbenzenesulfonic acid methyl esters (LABSA ME). The behavior of LAS and LABSA ME was studied under ascending high-performance thin-layer chromatography (HPTLC) using Kieselgel 60 F₂₅₄ and Sorbfil plates to purify extracts and preconcentrate analytes. A mixture of n-hexane with methanol (23 : 1, v/v) is proposed as a mobile phase. Under these conditions, sodium alkylbenzene sulfonates remain at the start line, while their derivatives (LABSA ME), obtained by methylation with trimethyl orthoformate in the presence of trifluoroacetic acid (yield η = 98%), form zones characterized by retention factors R_f of 0.62–0.71 on Kieselgel 60 F₂₅₄ and Sorbfil plates, respectively. The repeatability of R_f values is characterized by a relative standard deviation of 6.1 and 5.9%, respectively (n = 16). The completeness of the extraction (95.0–100.0%) of analytes from the plates is noted using descending HPTLC with acetonitrile. The applicability of the HPTLC method for preconcentrating analytes and purifying extracts is demonstrated using real water samples. Using GC–MS with electron impact ionization, concentrations of sodium alkylbenzene sulfonates were found in water sampled from the southern basin of Lake Baikal at a depth of 400 m (0.24 ± 0.02 µg/L) and in water obtained from melting snow collected from the ice of the Krestovka River at its mouth near the settlement of Listvyanka (31.1 ± 1.0 µg/L).