Development of Methodologies for Different Degrees of Resolution of Linear Alkylbenzene Sulfonates in Groundwater and Wastewater by Liquid Chromatography Using Sodium Dodecyl Sulphate

Abstract

Linear alkylbenzenesulfonates (LAS) are used extensively as surfactants in consumer formulations as a complex mixture of homologues and isomers. Separation of homologues and isomers of LAS is important in industrial and environmental samples in order to establish their behaviour. Here we present a HPLC methodology with fluorescent detection (FD) for the determination of the homologues and isomers as well as the sum of LAS present. The quantification of total LAS was achieved without a column, using the liquid chromatograph as a FIA system. The different homologues were separated using a Lichrospher-100 RP-8 column of 125 × 4 mm using a linear gradient of methanol and 30.0 mM sodium dodecyl sulphate (SDS), increasing the methanol content linearly from 55% to 70% in 16 min. The resolution of isomers was carried out by using two coupled Lichrospher-100 RP-18 columns of 250 × 4 mm. Elution of isomers was done with a gradient of flow rate from 1.0 to 0.25 mL min⁻¹ using a linear gradient of acetonitrile and 5.0 mM SDS increasing the acetonitrile content linearly from 20% to 40% in 160 min. The methods were validated and applied satisfactorily to the determination of LAS in urban wastewater and ground water.