Direct determination of leather dyes by visible reflectance spectroscopy using partial least-squares regression

A method for the simultaneous spectrophotometric determination of leather dyes based on their reflectance spectrum in the visible region and the use of partial least-squares regression (PLSR) is proposed. Calibration was done by using absorption, first- and second-derivative spectra for five sets of 29 different mixtures of Sellaset H dyes over the wavelength range 400-900 nm. The proposed multivariate calibration method allowed us to develop a model adjusted to the dye concentrations in the mixtures used at the calibration stage. The method was validated with five test sets consisting of eight samples each. The proposed method allows the accurate, highly expeditious quantitation of various dyes without the need for a prior extraction. The overall calibration and prediction errors were all in the region of 5.6-10.7 and 6.9-12.5%, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.