Ion-chromatographic characterization of ethoxylated anionic surfactants

Alkyl ether sulfates (AES), analyzed by nonsuppressed or single-column ion chromatography with conductivity detection, generate profiles that are characteristic of the ethoxylate content. Identification of ethoxylation content was accomplished by calculating the slope of the log of the peak area for each homologue vs. the number of ethoxyl groups in the homologue. Quantitation of ethylene oxide content as well as quantitation of mixed alkyl sufates in the presence of AES in mixed surfactant systems is possible. Raw materials require only dilution in mobile phase, while finished products must be subjected to a solid-phase extraction by means of a reverse-phase cartridge and an ion-pair reagent. The chromatogram of the anionic surfactant yields the moles of ethoxylation and the characterization of the ethoxyl chain distribution. Anionic surfactant mixtures in products are identified and quantitated by reference to AES raw materials with a similar slope.