Use of multivariate curve resolution for determination of chromium in tanning samples using sequential injection analysis

We report a method for determining total chromium in tanning samples using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. With a suitable analytical sequence CrO42 - is converted to Cr2O72 - inside the tubes of the SIA system, after total oxidation of chromium(III). A data matrix is obtained and analysed by several chemometric techniques based on multivariate analysis: principal components analysis, simple-to-use interactive selfmodelling mixture analysis, and multivariate curve resolution-alternating least-squares. We studied several samples from different stages of a tanning process. Two of these samples were easily oxidized but the others needed more extreme conditions. The analytical sequence prepared, which was based on obtaining a pH gradient and used H2SO4 as reagent, is valid and independent of the level of oxidation needed for the sample. We established a calibration model and evaluated the figures of merit. In some samples we found interferents. With this method the amounts of chromium in each sample were quantified and the results were statistically similar to those obtained by use of the reference method, atomic absorption spectrometry.