SPECTROPHOTOMETRIC METHOD OF DETERMINATION OF MICROAMOUNTS NIOBIUM IN NITRIC ACID WITH 5-Br-PADAP

In this method, the sample is first treated with H_2SO_4 to drive out the nitrateion, to keep niobium in the same valence state, and to avoid the adjustment ofpH. A violet blue ternary complex of niobium with 5-Br-PADAP and tartaricacid is then formed in a medium of tartaric acid. The composition of the complexis found to be Nb:5-Br-PACAP: Tar=1:1:1. The optimum pH for the complexformation is 1.0--3.0. The complex has an absorption maximum at 600 nm withε=5.7×10~4. Beer's law is obeyed for 0.699--14.0 μNb/ml.