Pesticide analysis by gas chromatography is a tedious process due the activity, thermal instability, and the prevalence of isomeric analyte species. Identification of these analytes, typically by mass spectrometry, also becomes taxing, since the ionization routes for many of the compounds result in low analyte response and similar spectra used for database identification. The vacuum ultraviolet detector which we have recently introduced is capable of measuring gas phase absorbance spectra within the wavelength range of 115-185 nm (VUV region) and up to 240 nm. Within this region, all species absorb energy and possess a unique spectral response, even for ionizably labile pesticides which limit mass spectrometry. Specifically, chlorinated pesticides have sections of fine structure absorbance throughout this wavelength range, further aiding to identification. The mass spectral responses for captafol, folpet, and methidathion have reported low spectral database matching capabilities for qualitative identification. The VUV absorbance of these pesticides, along with various others that are isomers, structurally similar, or tend to coelute, are very unique, allowing for confident identification and spectral deconvolution if analyte or matrix coelution occurs. The ability to deconvolute is demonstrated by quantifying captan under fast GC conditions used to reduce thermal decomposition on column and the coeluting pair of fenthion and chlorpyrifos.

Vacuum ultraviolet detection for the identification and quantification of pesticides by gas chromatography

248th National Meeting (2014)

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