Determination of alkylbenzene sulfonates in water by using phase extraction and vapor-phase esterification gas chromatography
Abstract
Linear Alkylbenzene Sulfonates (LAS) are an important class of anionic surfactants used as detergents for both industrial and domestic applications. LAS are released to the environment from waste water treatment, leaking septic tanks, and run off. LAS compounds are biologically reactive and have been found to have estrogenic properties. Despite the common occurrence of these compounds they are difficult to analyze in water and waste water. Colorimetric assay such as EPA 425.1 is simple to perform, but are not specific for LAS. Reversed phase liquid chromatography has been utilized for the analysis of these compounds but this method does not give good resolution of LAS components. Gas chromatography (GC) of LAS esters provides a high resolution separation of LAS compounds but the ester derivatives are not easy to quantitatively synthesize; Recently, some promising methods utilizing tetrabutylammonium ion pairs to esterify LAS during GC injection have been published. Vapor phase derivatization using tetrabutylammonium bisulfate (TBA) ion pair was investigated using a pyrolyzer type GC injector. The temperature dependence of this vapor phase derivatization and ester formation using TBA ion-pair reagent has been investigated. In this study an ion pair derivatization (flash-heater esterification) method using trialkylsulfonium and dimethylarylsulfonium cations instead of the tetrabutylammonium cation (TBA) has been developed. The synthesis of sulfonium cations has also been investigated. This project has produced a new analytical method for LAS using trialkylsulfonium and dimethylarylsulfonium cations. The method has utilized reversed phase extraction (SPE) methods for isolating extracting LAS from water. The LAS are then allowed to interact with the sulfonium salt, to form a sulfonium-LAS ion pair, which is then injected into a gas chromatograph to effect esterification and separation. Preliminary results from an analysis of water from Lake Mead are reported.