Analytical Sciences

Abstract − Analytical Sciences, 27(8), 845 (2011).

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.