Quantitative analysis of agrochemical formulations by multivariate spectroscopic techniques

Quantitative multivariate Fourier transform infrared (FT-IR) analysis has been compared with conventional gas chromatography and FT-Raman spectroscopy for the analysis of mixtures containing the organophosphate insecticide chlorpyrifos. Mid-IR spectra were recorded with the use of a ZnSe attenuated total reflectance (ATR) cell; Raman spectra were recorded on samples contained in glass sample bottles. Simple homogeneous solutions in either trimethylpentane or the commercial complex aromatic solvents Solvesso 100 or Solvesso 150 give results by FT-IR spectroscopy which are of a quality similar to those obtained by a conventional gas chromatographic technique. It is found that the multivariate FT-IR approach gives a rapid indication of the presence of impurities in the mixture, e.g., of surfactants or of the thermal degradation product 3,5,6-trichloro-2-pyridinol. Chlorpyrifos may be determined in the presence of its analog chlorpyrifos-methyl, but not if it is at a concentration that is too low relative to the analog, Variations in the spectral data on changing the temperature have been successfully modeled in terms of variations in the refractive index and density of the solutions. Multivariate FT-Raman spectroscopy appears less applicable to the formulation containing the aromatic solvent systems investigated, largely because the solvents used are too strongly scattering.