Research on Surface Sampling for Determination of Pesticide Residues in Pome Fruit

A surface sampling method for analysis of pesticide residues in pome fruit was studied by layer-by-layer scan from pericarp to kernel. Phoxim residues of apples, pears and papayas was determined by GC-MS, respectively, in core, different layers of pulp, peel ,as well as the whole fruit. Phoxim residue content was decreased when depth of the layer increased. It was inferred from experimental data the the appropriate depth of surface sampling is 2.5mm, 2mm and 3.5mm in apples, pears and papayas. Although the ratio of the pesticide in pericarp and the total (Cp/Ct) ranged from 6.241 to 9.262 in apple, 4.254 to 5.069 in pears, and 4.39 to 5.037 in papayas in different groups, the ratio of Cp/Ct and quality of specific group is essentially unchanged for a certain kind of fruit. According to the results, a conversion formula of the content of pesticide residues in whole fruit and pericarp was set, based on surface sampling method.