Spectrophotometric method for the determination of an anionic surfactant without liquid–liquid extraction

A simple method for spectrophotometric determination of an anionic surfactant (0–15 μg) was studied. The ion associate formed between sodium dodecyl sulfate (SDS) and Rhodamine 6G was adsorbed onto the wall of a PTFE vessel by vigorous shaking. After the resultant solution was discarded, the ion associate was dissolved in methyl cellosolve and its absorbance measured at 534 nm. The apparent molar absorptivity for SDS was 8.5×104 l mol−1 cm−1. The coefficient of variation for the determination of 7.2 μg of SDS in 10 ml of sample was 4.5% (n=6). Greater sensitivity could be achieved by using a 50 ml sample.