Simultaneous determination of cationic and nonionic surfactants in consumer products by use of mixed aggregate-based methodology

Abstract

Mixed aggregate-based methodology was used for the simultaneous resolution of differently charged surfactants in binary mixtures. The new approach relies on the sequential formation of two types of surfactant aggregates in an aqueous medium, premicelles and micelles, and on measurement, in a single run, of two parameters related to the formation they provide. Premicelles can be easily induced for ionic surfactants in the presence of oppositely charged dyes. In this work, the simultaneous resolution of cationic dialkyldimethylammonium (DDAS) and nonionic alkoxylated (NAS) surfactants in binary mixtures was undertaken. The anionic surfactant sodium dodecyl sulfate (SDS) was used as titrant and the anionic dye Coomassie Brilliant Blue G (CBBG) to induce DDAS premicellar aggregates. Measurement of the total amount of CBBG–DDAS–SDS premicellar aggregates and the critical micelle concentration (c.m.c.) of DDAS–NAS–SDS micelles permitted us to determine the total concentration of DDAS and NAS at the ng ml⁻¹ level in a single run with relative errors of less than 5% in most instances. The simultaneous determination of cationic and nonionic surfactants in commercially available softeners was accomplished without the need for sample treatment. The results obtained indicate that this methodology possesses a high potential for quality control of surfactant formulated products.