Quantitative nuclear magnetic resonance spectrometry II. Purity of phosphorus-based agrochemicals glyphosate (N-(phosphonomethyl)-glycine) and profenofos (O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phosphorothioate) measured by ~1H and ~(31)P QNMR s

摘要

The purities of the widely-used herbicide glyphosate (N-(phosphonomethyl)glycine), and the insecticide profenofos (O-(4-bromo-2-chlorophenyl) O-ethyl S-propyl phosphorothioate) were determined by ~1H and ~(31)P quantitative nuclear magnetic resonance (QNMR) spectrometry using an internal standard. QNMR does not need a standard reference of the same target analyte, in contrast to chromatographic methods, but only a compound containing the nucleus of interest. Sodium acetate and sodium phosphate of known purity were chosen as internal standards for ~1H NMR and ~(31)P NMR), respectively for the water soluble glyphosate and a single internal standard, trimethyl phosphate for both ~1H and ~(31)P NMR quantitative analysis of the organic soluble profenofos. These standards have NMR peaks that do not interfere with those of the analyte, they are chemically inert and are soluble in the deuterated solvent. The average purity of glyphosate obtained by ~1H NMR (97.7%, sigma = 0.68) agreed with that by ~(31)P NMR (96.53%, sigma = 0.90; ANOVA, P = 0.074) for the five batches provided by the manufacturer according to the procedurer for chemical registration in Australia. The standard deviations of seven independent analyses of a single batch by ~1H NMR and ~(31)P NMR were sigma = 0.24% and sigma = 0.33%, respectively, values which confirm the exceptional precision of the method. The purity of profenofos by ~1H NMR (94.63%, sigma = 0.14) also agreed with that by ~(31)P NMR (94.62%, sigma = 0.59; ANOVA, P = 0.97). Uncertainty budgets for the measured purities of glyphosate and profenofos show that the uncertainty in the purity of the internal standard is a major contributor to the uncertainty of the result. NMR was also used to establish the impurity profile of both compounds, and quantify the impurities present.