INDIRECT AAS DETERMINATION OF ANIONIC SURFACTANTS BY FORMATION OF AN ION-PAIR WITH BIS(2-BENZOYL PYRIDINE THIOSEMICARBAZONE)COBALT(III)

An indirect atomic absorption spectrometric (AAS) determination of anionic surfactants, viz., sodium dodecyl sulphate (SDS) has been described. The method utilizes the formation of ion-association pair of SDS with [Co(BPTC)(2)](+) (where BPTC = 2-benzoyl pyridine thiosemicarbazone), extraction of the complex into iso-pentyl acetate-iso-pentyl alcohol mixture (8.5:1.5) within the pH range 3.1-9.5, aspirating the organic phase into flame AAS and measuring the cobalt signal at 240.7 nm, and hence indirectly determining the anionic surfactant concentration. The method gave a linear calibration plot for anionic surfactant over the range 0.5-33 mu g mL(-1) accompanying a limit of detection (3 sigma) of 18 mu g mL(-1). The proposed method is free from a large number of interfering metal ions, anions and organics. The method has been successfully applied to the determination of anionic surfactants (in terms of SDS) in toothpastes, commercial liquid detergents and waste water samples with a relative standard deviation (RSD) of 3.5, 4.8 and 1.7%, respectively. The sensitivity of the method has further been increased using graphite furnace atomic absorption spectrometry,