Application of gas chromatography negative ion chemical ionization mass spectrometry in confirmatory procedures for pesticide residues

Both the advantages and limitations of gas chromatography negative ion chemical ionization (NICI) mass spectrometry arise from the technique's close similarity to gas chromatography using a conventional electron capture detector (ECD). The specificity of both techniques arises from the wide range of response factors from different compound classes. However, the fact that almost every compound has some electron capture response is the reason the ECD has the reputation of being the least specific of the specific detectors for pesticide residue analysis. Moreover, while good ECD response means good NICI response, it does not guarantee sufficient negative ion mass spectral data for confirmatory purposes. The applications presented in this paper illustrate both the advantages and limitations of the technique. The most obvious applications are straightforward extensions of gas chromatographic ECD methods of analysis as illustrated in the gas chromatographic NICI analysis of pendimethalin, a dinitroaniline herbicide, at the pg level. The use of gas chromatography NICI as a confirmatory technique to complement a gas chromatographic method using a flame photometric detector is shown in the analysis of fosthietan, an organophosphate pesticide, in corn tissues. The gas chromatographic NICI analysis of sulfamethazine residues in cattle and swine tissues exemplifies that good ECD response does not guarantee satisfactory negative ion mass spectral data for confirmatory purposes.