β-correction as a preprocessing method for partial least squares in simultaneous determination of zinc and lead

An error analysis of predicted values using spectral correction matrix and partial least squares (PLS) modeling is applied for the determination of Zn2+ and Pb2+ with methylthymol blue (MTB) as a metallochromic indicator. The concentration ranges for Pb2+ and Zn2+ in standard solution sets are 0.5-5.2 and 0.1-2.5 mug ml(-1), respectively. The experimental calibration set was composed of 20 sample solutions using a random design for two component mixtures. The absorption spectra were recorded from 400 to 700 nm. The two wavelengths, which exert the minimum error in prediction of two metal ion concentrations, are chosen according to an error analysis of different pairs of wavelengths. The effect of the pH on the sensitivity in determination of Zn2+ and Pb2+ using MTB was studied in order to choose the optimum pH (pH = 6) for determination. The values of root mean square difference (RMSD) for lead and zinc using beta-correction partial least squares were 0.0977 and 0.1266. respectively. The effect of diverse ions and several experimental parameters were studied. The method was used for the determination of lead and zinc in alloy samples. (C) 2004 Elsevier B.V. All rights reserved.