Uncertainty analysis of multi residue methods for pesticides in Lettuce

Two methods were developed for uncertainty analysis in lettuce using different processing conditions. Methodology I involved analysis through analytical portion sizes of 5, 15, 50 and 150g which were processed at ambient and low temperature processing conditions. 50 and 150g samples recovered a low percentage (68-72%) of pesticides as compared with 5 and 15g (64- 78%) samples. The uncertainty was lowest for 50g samples at ambient temperature and for 15g samples at low temperature processing. 30g analytical portion size was decided to be analyzed through methodology II, resulting in higher recoveries (70-111%) and lower uncertainty (below 11%). The uncertainty and sampling constant determined from internal standard chlorpyrifos was within limit and the pesticide was stable during analysis. The processing of samples at low temperature (i.e., cryogenic milling) was more efficient for the analysis of pesticide residues.