Cow Brand Soap Kyoshinsha Co., Ltd.

A new method for analyzing ionic and nonionic surfactants present in shampoos and hair-conditioners is proposed; a combination of the ordinary spectrophotometry with differential refractometry as the detector or reversed-phase HPLC was used.A ratio of the area intensity of the UV absorption to that given by differential refractometry (UV/RI ratio) was specific to each surfactant.When the UV/RI ratios were plotted against the retention time (Rt) for various authentic surfactants, location of a spot in the UV/RI-vs.-Rt map was specific to each surfactant and there was no overlapping between spots even for two similar surfactants which are usually overlapped in the UV-vs.-Rt map.Accordingly, the UV/RI-vs-Rt map obtained for an arbitrary mixture of surfactants allowed more accurate anal. of surfactants than the ordinary method based solely on the retention time.In fact, when model shampoos and hair-conditioners using anionic, cationic, amphoteric and nonionic surfactants were analyzed with MeOH-H₂O as a mobile phase on the ODS column, the anal. values from the present method were quant. successful.