Application of nuclear magnetic resonance spectroscopy to the identification and quantitation of pesticide residues in soil

Abstract

The application of high-resolution Fourier-transform nuclear magnetic resonance (NMR) spectroscopy to the identification of metabolites of the phosphorodithioate ester pesticide sulprofos (Bolster) was investigated. While differentiation between the various metabolites using either or 13C NMR was unsuccessful, 31P NMR proved to be an exquisitely sensitive probe for these compounds. Treatment of soil samples with sulprofos at a concentration of 7.4 ppm, followed by incubation for up to 90 days, led to the formation of two major metabolites. The residues were extracted, characterized, and quantitated using 31P NMR. Use of 14C radiolabeled material and analysis of extracts by high-performance liquid chromatography and liquid scintillation counting confirmed the results obtained by 31P NMR.

Environmental NMR – the early years

“…With improvement in NMR instrumentation, 31 P NMR was applied to the analysis of organophosphorus insecticide residues in cole crops, although further improvement in sensitivity and peak identification was considered necessary for routine analysis. The utility of 31 P NMR has also been demonstrated for the identification and quantification of pesticide residues in soil and for the detection and analysis of chemical warfare agents . A systematic evaluation of quantitative 31 P NMR established protocols and recommended wider application by regulated industries such as pharmaceutical and agricultural chemical businesses …”

Use of NMR techniques for toxic organophosphorus compound profiling

“…OP compounds can also undergo enzymatic degradation in the environment. The application of NMR spectroscopy in the analysis of pesticide metabolism in soil was reported by Krolski et al [124]. They studied the metabolic degradation of 13 C-labeled sulprofos (O-ethyl O-4-(methylthio)phenyl S-propyl phosphorodithioate) in biologically active sandy loam.…”

“…The examination of the samples extended over a period of several years, and the authors were able to present the predominant as well as the secondary modes of degradation of methyl parathion (O,Odimethyl O-4-nitrophenyl phosphorothioate) and chlorpyrifos. A related application of 31 P MAS NMR in CWA degradation studies Reprinted with permission from [124]. Copyright 1992 American Chemical Society.…”

NMR Investigation of the Behavior of an Organothiophosphate Pesticide, Chlorpyrifos, Sorbed on Soil Components

“…The phenolic oxygen is expected to be predominantly in the -OH form, considering the relative pKa values (1.49 and 4.55, respectively) of diethyl thiophosphoric acid and 3,4,6trichloro-2-pyridinol (20). The results suggest that 13 C CP-MAS experiments should be able to distinguish chlorpyrifos from the aryl hydrolysis product by detection or absence of the aromatic peak at about 164 ppm, but 13 C CP-MAS experiments were not pursued in depth, as they suffer from substantially lower sensitivity than corresponding 31 P experiments (21) and because 31 P chemical shifts are more sensitive to anticipated structural changes during pesticide decomposition than are 13 C chemical shifts (22). Also, 31 P NMR does not suffer spectral interference problems with the organic constituents of soil.…”

“…31 P NMR analysis of the DMSO-d6 extract of the sample represented in Figure 3C and D (Figure SI-1B) indicates that the extract consists mostly of unreacted chlorpyrifos (62 ppm), although at least three other peaks are seen: a substantial peak at 28 ppm probably represents S,O-isomerized chlorpyrifos (either structure IV or V), a small peak at 53 ppm is probably hydrolyzed chlorpyrifos (II; diethylthiophosphoric acid), and a small peak at about 49 ppm may represent either III or a product resulting from additional hydrolysis of II or III, e.g., O-ethyl thiophosphoric acid (VII). 31 P chemical shifts in the 40-100 ppm range are seen (Table 1) for structures of the type SdP(OR′)3, where R′ is an alkyl or aryl group, whereas structures containing OdP give rise to shifts in the 35 ppm to -25 ppm range (7,22,27).…”