Estimation of precision and efficiency mass transfer steps for the determination of pesticides in vegetables aiming at the expression of results withreliable uncertainty

A 'bottom-up' approach for the expression of results obtained from analytic al methods that include analytical steps with recovery inherently different from 100% [mass transfer steps (MTS): extraction, evaporation, clean-up pr ocedures, digestion, etc.] is presented. The estimation of the combination of all MTS uncertainty involves the comparison of the experimental dispersi on of replicated analyses of spiked samples with the estimation of the unce rtainty obtained for the combination of all uncertainty sources except MTS ones ('incomplete' estimation). The estimation of MTS uncertainty by differ ence is performed after evaluating the statistical difference between the ' incomplete' estimation and the experimental dispersion (F-test). When the t wo estimations are statistically equivalent, the MTS uncertainty is conside red to be negligible in relation to the other sources budget. The assumptio n of constancy of MTS performance within the analytical range is tested thr ough single analyses at several concentration levels and is evaluated by th e inclusion of the expected values at the intervals resulting from the comb ination of the MTS uncertainty estimation performed at one concentration le vel and the 'incomplete' estimation. The developed methodology can also be useful for method optimisation and validation and for the detection of smal l trends in results. The determination of pesticides in sweet peppers by GC -NPD was used to explore the above concepts.