Improved Method for Determination of Anionic Surfactant in Water by Methylene Blue Spectrophotometry

The method for the determination of anionic surfactant in water by methylene blue spectrophotometry (GB 7494—1987) had been improved. Chloroform was replaced by dichloromethane as the extractant, which was relatively less toxic. The test tube replaced the separating funnel, and the oscillator was used for extraction. It was shown that the best extraction time of the improved method was 1.5 min, and the analysis time of a single sample was less than 10 min. The linear range of the standard curve for sodium dodecyl benzene sulfonate was within 2.0 mg·L^-1, with detection limit (3s/k) of 0.029 7 mg·L^-1. The standard solutions of sodium dodecyl benzene sulfonate were determined for 6 times, and RSDs (n=6) of the determined values were less than 9.0%. Test for recovery was made on blank sample by standard addition method, giving results in the range of 95.0%-99.1%.