Spectrophotometric determination of bismuth and EDTA by means of the reaction of bismuth with pyrocatechol violet in the presence of septonex

The reaction of bismuth(III) with Pyrocatechol Violet in the presence of the cationic surfactant Septonex was studied and the optimal conditions for its analytical use were found (lambda = 612 nm, pH = 3.1, C(PV) = 4 x 10(-5)M, C(Sept), = 5 x 10(-4)M). The Lambert-Beer law is obeyed over the bismuth range 0.1-7.5 mug/ml. Decomposition of the Bi-PV-Septonex complex was utilized for indirect determination of ethylenediaminetetra-acetic acid at concentrations of 0.3-7.4 mug/ml.