Univariate and Multivariate Calibration for the Quantitative Determination of Methyl-Parathion in Pesticide Formulations by FT-Raman Spectroscopy

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Abstract
A Fourier transform (FT)-Raman method for the quantitative determination of methyl-parathion in pesticide formulations is described. The proposed method was applied to the analysis of formulations of methyl-parathion. Univariate and multivariate calibration were used and compared for quantitative analysis. Bands observed at 634, 661, 1113, 1348, and 1527 cm−1 were used for univariate calibration. Calibration curves were linear (correlation coefficients: 0.996–0.998 and 0.994–0.999 for band intensity and band area measurements, respectively) in the concentration range of 0.6–3.75 M for the 634, 661, and 1527 cm−1 bands; 0.05–3.75 M for the 1113 cm−1 band; and 0.1–3.75 M for the 1348 cm−1 band. Precision ranged from 0.5 to 5.2% and 0.1 to 6.8% relative standard deviation (RSD) ( n = 4) for band intensity and band area measurements, respectively. Spectra normalization against the 802 cm−1 cyclohexane band improved the long-term stability of calibration, allowing the use of calibration data acquired 30 days prior to analysis. The application of the method was extended through multivariate calibration by multiple linear regression using the 858 and 2952 cm−1 bands. Results obtained compare well with those obtained by the high-performance liquid chromatography (HPLC) reference method. The FT-Raman method developed is rapid, simple, and safe, as toxic samples are analyzed “as received” without sample pretreatment.