Solvent extraction/ spectrophotometric determination of anionic surfactants in seawater

Abstract

Solvent extraction and spectrophotometric determination of an anionic surfactant, sodium laurylsulfate (SLS), in seawater was examined with Ethyl Violet (EV) as a counter ion. At pH 4.9, this surfactant reacts with EV to form an ion-associate, which can be extracted with toluene. Chloride ion also forms an ion-associate with EV and is extracted simultaneously with SLS. To eliminate the chloride interference, the organic phase was washed with dilute hydrochloric acid solution. The concentration of the surfactant can be determined by measuring the absorbance of the extract at 612 nm after back washing. Calibration cuve is linear over the range 02.0×10^-5 M (in toluene) of the surfactant and the apparent molar absorptivity is 92500 1 mol^-1 cm^-1. The recommended procedure is as follows: Take 100 ml of the sample solution containing the surfactant up to 1.0×10^-6 M in 0.5 M sodium chloride solution in a 100 ml separatory funnel. Add 5 ml of 1 M sodium sulfate, 1 ml of 0.1 M EDTA solution, 2 ml of acetate buffer solution (pH 5) and 3 ml of 8.8×10^-3 M EV solution and mix well. Shake the content with 5 ml of toluene for 35 min. After complete phase separation, the organic phase was washed with 50 ml of 0.08 M hydrochloric acid and the absorbance in toluene was measured at 612 nm against a reagent blank. Free from interferences from major constituents of seawater, this proposed method can be applied to the determination of surfactants in seawater.