An Ion-Pair Extraction Detector for the Liquid-Chromatographic Determination of Anionic Surfactants

Abstract

A sensitive method for the analysis of different classes of anionic surfactants based on alkyl (ether), alkylphenol (ether) and alkylbenzene formulations by means of high-performance liquid chromatography (HPLC) is described. A solvent-segmented post-column ion-pair extraction system is used to detect surfactants containing sulphate, sulphonate or sulphosuccinate as the anionic group. HPLC is carried out with silica SI-60 as the stationary phase and mixtures of tri-chloromethane and ethanol containing a crown ether as the mobile phase. The column effluent is mixed with an aqueous acidic solution of the fluorogenic acridinium cation. The ion pairs formed between the anionic compounds and acridinium (Acr) are extracted into the organic phase, which then is separated from the aqueous phase and monitored fluorimetrically. At optimum flow-rate conditions the contribution to peak broadening due to the extraction system, measured as half peak width at half height, is about 50μl. The detection limits are at the low ng-nevel for plug injection, and from 10 to 400 ng in analysis by HPLC.