Simultaneous analysis of anionic, amphoteric, nonionic and cationic surfactant mixtures in shampoo and hair conditioner by RP-HPLC/ELSD and LC/MS

A simple and simultaneous analysis method for four (anionic, amphoteric, nonionic, and cationic) classes of surfactants in shampoo and hair conditioner was newly developed. Analysis of the surfactants was performed using a reversed-phase HPLC (RPLC) combined with evaporative light scattering detection (ELSD) without any pre-treatment. An optimum analysis condition for the resolution of both four main surfactant mixtures used in shampoo and five main surfactants used in hair conditioner could be established under a gradient mobile phase condition with acetonitrile, tetrahydrofuran and water. The detection limits were 2.5-30 μg mL^-1 except for SLES (150 μg mL^-1), and the calibration curves, i.e. the log-log plots, were linear in the working range of 2.5-5250 μg mL^-1 with R² values of above 0.998. The observed precision was less than 5% R.S.D. The elution peaks were identified by a liquid chromatography-mass spectrometer (LC-MS) equipped with an electrospray interface operating in mixed-mode.