Precise and rapid determination of amphoteric and nonionic surfactants by 1H nuclear magnetic resonance using an internal standard

A method based on proton nuclear magnetic resonance (1H-NMR) using an internal standard (IS) was developed for the determination of amphoteric and nonionic surfactants. This method does not require a tedious pretreatment, and surfactants are determined by using integrations of IS and diagnostic surfactant resonances in the 1H-NMR spectrum. By optimizing the combination of solvent and IS, various surfactants were determined under the same condition. Each sample was measured within 5 min, and the detection limit given for lauryl dimethylamine oxide, a typical amphoteric surfactant, was 8.0 ppm. The results obtained for commercial surfactants were in good agreement with those of the conventional methods (gravimetric method etc.) and the relative standard deviations were 0.13∼0.36%. Furthermore, we confirmed that the proposed method was applicable to the determination of nonionic surfactants not containing an ethylene oxide chain, such as glycerol fatty acid ester and fatty acid alkanolamide.