An orthogonal signal correction – genetic algorithm – partial least squares (OSC-GA-PLS) was developed for the simultaneous spectrophotometric determination of lead and mercury in different types of water samples by 4-(2-pyridylazo) resorcinol as the chromogenic reagent in water media. The effects of pH and 4-(2- pyridyalzo) resorcinol concentration on the complexes formation reactions were studied. The simultaneous determination of lead and mercury mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. The PLS modeling was used for the multivariate calibration for the spectrophotometric data. OSC is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis and GA is a suitable method for selecting wavelength for PLS calibration. In this study, the calibration model is based on absorption spectra in the 450 – 550 nm range for 25 different mixtures of lead and mercury. Calibration matrices were containing 0.05 – 1.05 and 0.05 – 1.15 μg mL-1 of lead and mercury, respectively. The RMSEP for lead and mercury with PLS, OSC-PLS and OSCGA- PLS were 0.0664 and 0.0504, 0.0329 and 0.0230, and 0.0105, 0.0061, respectively. This procedure allows the simultaneous determination of lead and mercury in water samples and good reliability of the determination was proved.
