Degradation of methamidophos on soultanina grapes on the vines and during refrigerated storage

Decomposition of the pesticide methamidophos was studied in an experiment in field-sprayed grapes of the Soultanina variety. Residues were studied by a simple gas-chromatographic method, using a glass capillary column and NP detector. The decomposition of methamidophos was studied in grapes remaining on the vines after spraying in open and covered vineyards, in grapes harvested and stored in a refrigerated room and in grapes dried into raisins. The recovery of methamidophos was 96.2–112%. The relative standard deviation (RSD) was between 1.4 and 6.2%. The detection limit was 0.02 mg/kg. The results show that, there exists a delayed residue decline during post-harvest storage compared to that for grapes remaining on the vines. From the experimental results, best fit curves were determined and kinetic equations, rate constants and half-lives were calculated. Half-lives found were 16 days for grapes on uncovered vines, 22 days for covered vines and 267 days for grapes stored in a refrigerator. Concentration of methamidophos in raisins was three times higher than that in grapes.