The determination of anionic detergents with iron (II) chelates: application to sewage and sewage effluents

Abstract

The cationic species ferroin is proposed for the determination of microgram amounts of anionic detergents by absorptiometry, and the development of the method is described. For application to samples in aqueous solutions, the ferroin reagent has an iron(II) concentration of 50 p.p.m. and a molar excess of 1,10-phenanthroline of from 5 to 6. For sewage analysis, the reagent contains 500 p.p.m. of iron(II) and has a 1,10-phenanthroline-to-iron(II) ratio of 2·5. A typical precision for aqueous solution samples is ±1·4 per cent. and for sewage samples ±3·7 per cent. The results for sewage samples have been compared with those by the routine methylene-blue method. Interferences of common ions have been studied and the method has been used to assess the relative purity of three anionics used as reference standards. Some advantages of ferroin over methylene blue are suggested.

Ferroin reagents should be replaced by iron(II)-bipyridyl reagents when samples contain more than a few p.p.m. of thiocyanate.