A new spectrophotometric method for the determination of total and ferric iron in rain water at the ppb level

A new, simple, selective and sensitive spectrophotometric procedure for the on-site quantification of iron at nano-gram levels in atmospheric precipit ations, i.e. rain as sample source is described. It is based on the color r eaction of Fe3+ with SCN- ions in the presence of a cationic surfactant, i. e. cetylpyridinium chloride (CPC), in strong HCl solution, and subsequent e xtraction of the complex with N-octylacetamide into toluene or chloroform. The apparent molar absorptivity of the complex is 2.60 x 10(5) L mol(-1) cm (-1) at lambda (max) = 480 nm at an enrichment factor (EF) of 10. The detec tion limit (causing higher absorbance than the sum of the blank absorbance (0.009) and 3 SD) is 5 ng mL(-1) Fe. Ions commonly associated with iron did not interfere in the present method. The effect of analytical variables, i .e. amount and type of the reagents, acidity, solvent, temperature, dilutio n, etc., in the determination of iron are discussed. The validity of the pr esent method is checked with GF-AAS. The method has been applied to the det ermination of iron at the ppb level in rain water samples.