Criteria for selecting analytical wavelengths for multicomponent mixtures by the CPA matrix method and simultaneous spectrophotometric determination of niobium and tantalum

The reversed matrix representation of the Lambert-Beer law (CPA matrix method) is applied in simultaneous spectrophotometric determinations. Restrictions on the selection of analytical wavelengths in applying the CPA matrix method are investigated experimentally and theoretically. Four criteria for selecting suitable wavelengths are described. A spectrophotometric procedure for niobium and tantalum with salicylfluorone and cetyltrimethylammonium bromide in the presence of tartaric acid was developed and used for the simultaneous determination of niobium and tantalum by the CPA matrix method. The absorption maxima were at 520 and 513 nm, respectively. Measurements at six wavelengths in the range 500–530 nm provided data from which niobium (0.04–0.4 μm ml^?1) and tantalum (0.08–0.8 μg ml^?1) were evaluated, with relative standard deviations of <2.