Factor analysis–spectrophotometry for the simultaneous determination of valence states of metals

Abstract

Two Mⁿ⁺–2-(5-bromo-2-pyridylazo)-5-diethylaminophenol systems for the simultaneous determination of the valence states of Cr and Fe using factor analysis were studied. (1) At pH 4.0, Cr^III and Cr^VI react with the reagent to form stable complexes and a slight difference in the wavelengths of maximum absorption (λ_max.) between the two complexes is observed when the sodium lauryl sulfate, which also acts as a solubilizing and sensitizing agent, is added, viz., 590 nm for Cr^III and 593 nm for Cr^VI complexes. (2) In the presence of ethanol, both Fe^II and Fe^III form 1:2 complexes with the reagent at pH 2.5–3.5 and the λ_max. of the Fe^II and Fe^III complexes is at 557 and 592 nm, respectively. In the target transformation factor analysis, the K coefficients calculated from the standard mixtures by classical least-squares analysis and a non-zero intercept added to each wavelength are used as the target vector instead of the pure component standards; this can decrease the analysis errors introduced by the interaction between the two species and by deviations from Beer's law.