[en] A study was made on extraction of ion associates of niobium complex acids with pyrocatechol(R)derivatives and basic dyes(D). The best results were obtained when using tetrabromopyrocatechol and brilliant green. It is shown that the degree of associate extraction depends on medium acidity and anion background; optimal conditions: 0.2-0.9 M H₂SO₄ and 0.25-1.35 M HCl. 10-fold D excess and not less than 100-fold R excess are required for complete Nb binding in associate. Component ratio in formed associate is Nb:R:D=1:2:2. Ta prevents spectrophotometric Nb determination under optimal conditions. If acidity is increased up to 1.8-2.0 M HCl, Nb can be determined in the presence of 7-fold Ta excess and in the presence of 100-fold amounts of Zn, B, Al, Ga, In, Tl, Ge, Sn, Zr, Hf, Sb, Mo, W but comparable Ti amounts prevent this. The developed technique can be used for determining 1-10 μg Nb in high-pure substances