Ion-pair extraction and fluorimetric determination of cadmium with cryptand 2.2.1 and eosin.

A method is described for the direct spectrofluorimetric determination of ultratraces of cadmium by extraction into 1,2-dichloroethane of the ion-pair formed between the eosinate anion and the cationic complex of Cd(2+) with cryptand 2.2.1. The detection limit for cadmium is 0.5 ng/ml, and the linear working range is from the detection limit to 150 ng/ml. The relative standard deviation is 1.5% at the 100 ng/ml level. The equilibrium constant has been estimated and refined by the Letagrop-DISTR program. The proposed method has been tested in the determination of cadmium in high-purity zinc. The results show good agreement with those found by the more common ICP emission photometry and anodic stripping voltammetry methods.