A comparison of dimethoate degradation in lemons and mandarins on the trees with two GC systems

Dimethoate was applied onto lemon and mandarin trees according to manufacturer instructions. Samples of 3 kg of each fruit were collected 2 h after spraying and then after 1, 6, 15, 21 and 28 days. Samples of the whole fruit and of the edible interior were analysed by GC, using two different capillary columns and with a nitrogen–phosphorus detector (NPD) and a flame photometric detector (FPD). Average recoveries were from 89 to 106% for lemons and from 85 to 108% for mandarins with RSD from 2.6 to 7.2% and from 2.2 to 8.5%, respectively. The method limit of determination was 0.01 mg/kg. Half-lives of dimethoate disappearance in whole fruit were 16.7 days for lemons and 30.1 days for mandarins. Relevant half-lives on the edible part were 11 and 14.2 days, respectively. Results from the two detector systems were almost equivalent.