ACCREDITATION AND QUALITY ASSURANCE, vol.13, no.2, pp.91-99, 2008 (SCI-Expanded)
The estimation of the uncertainty of measurement has, nowadays, become an integral part of analytical results. The uncertainty and efficiency of extraction and cleanup are very important components of a pesticide residue analytical method. In this work, for a quick review of extraction and cleanup efficiency and to evaluate the individual analysis steps during method adaptation, (14)C-carbaryl was applied at all fortification levels. Then, further analyses, such as ethylacetate extraction, filtration, evaporation and cleanup, were performed. The calibration of gel chromatograph column, performed with both (14)C-carbaryl and fortification mixture (dichlorvos, malathion and chlorpyrifos), showed that pesticide fractions came through the column between the 8- and 23-mL fractions. The overall recovery of (14)C-carbaryl after the extraction and cleanup step was 0.91, with the relative uncertainty of 0.084. Using the "bottom-up" approach, the uncertainty of extraction u(cEX) and cleanup u(cGPC) were 0.033 and 0.107, respectively. The combined standard uncertainty u(c) associated with the described analytical method was 0.112. Similar values were obtained using the alternative "top-down" approach: uncertainty of extraction u(ct1) was 0.039, uncertainty of cleanup u(ct2) was 0.108 and the combined standard uncertainty u(cAV) was 0.081. Both approaches showed that the uncertainty of cleanup was the main source of combined standard uncertainty.