Sorption-desorption photometric determination of trace iron in sodium, potassium, and ammonium thiocyanates using polyurethane foams

A reagent-free sorption photometric method for determining trace iron(III) in alkali-metal and ammonium thiocyanates was developed. The method consist s in the adsorption of iron(III) thiocyanate complexes on polyurethane foam s at pH 2-3 followed by the desorption of complexes with acetone and a meas urement of the absorbance of solutions. The analytical range for iron was 0 .5-20 mug in a 0.2-2.5-g portion of salt. The determination limit and relat ive standard deviation were 2 X 10(-5)% and 20-30%, respectively (n = 3; P = 0.95). The specific feature of the determination is that an additional ph otometric reagent is not introduced in the solution of the salt to be analy zed, because thiocyanate, that is, the matrix component of the test sample, acts as such a reagent.