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SENA, Marcelo M.; COLLINS, Carol H.; COLLINS, Kenneth E. and SCARMINIO, Ieda S.. Chemometric methods applied to the speciation of aqueous Cr(VI) solutions. Quím. Nova [online]. 2001, vol.24, n.3, pp.331-338. ISSN 0100-4042. http://dx.doi.org/10.1590/S0100-40422001000300009.
The equilibria, the spectra and the identities of the species of Cr(VI) that are present in aqueous solution have long been an active subject of discussion in the literature. In this paper, three different chemometric methodologies are applied to sets of UV/Visible spectra of aqueous Cr(VI) solutions, in order to solve a chemical system where there is no available information concerning the composition of the samples nor spectral information about the pure species. Imbrie Q-mode factor analysis, followed by varimax rotation and Imbrie oblique projection, were used to estimate the composition of Cr(VI) equilibrium solutions and, by combining these results with the k-matrix method, to obtain the pure spectra of the species. Evolving factor analysis and self modeling curve resolution were used to confirm the number of the species and the resolution of the system, respectively. Sets of 3.3´10-4 and 3.3´10-5 mol L-1 Cr(VI) solutions, respectively, were analyzed in the pH range from 1 to 12. Two factors were identified, which were related to the chromate ion (CrO42-) and bichromate ion (HCrO4-). The pK of the equilibrium was estimated as 5.8.
Keywords : chromium(VI); chemometrics; Imbrie Q-mode factor analysis; evolving factor analysis; self modeling curve resolution; equilibrium pK.