Analytical Sciences

Spectrometric Determination of Anionic Surfactants in Environmental Waters Based on Anisole Extraction of Their Bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) Ion Pairs

Yukio YOKOYAMA, Eriko TAI, and Hisakuni SATO

Department of Analytical Chemistry, Faculty of Engineering, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan

A spectrometric method for the determination of anionic surfactants in environmental water samples using the [Co(III)-(5-Cl-PADAP)₂]⁺ chromophore was technically improved for practical use. An anisole-extraction procedure was alternatively introduced and optimized in place of the earlier benzene-extraction procedure. The molar absorptivity for SDS found by the Co(III)-5-Cl-PADAP/anisole method was 72000 L mol⁻¹ cm⁻¹ at 560 nm, which was ca. 1.3-times higher than those by the Co(III)-5-Cl-PADAP/benzene method. The analytical sensitivity was almost independent of the kind of anionic surfactants. The calibration lines for SDS, LAS, and SSS were all linear between 1.0 × 10⁻⁷ and 1.0 × 10⁻⁵ mol L⁻¹ with acceptable r² values of 0.9998, 0.9995, and 0.9999, respectively. The method was applied to the analyses of river, well, and seawater samples, providing the compatible results by means of the standard-addition method. In the case of seawater, a phase-washing treatment of the extracted species using dilute HCl was effective to decrease the high blank absorbance. The Co(III)-5-Cl-PADAP/anisole method, showing no glass-adsorption problem, is more advantageous than the methylene-blue and ethyl-violet methods.

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