Abstract

AHUMADA, Diego A et al. Comparison of two approaches to estimate the uncertainty for pesticide residue analysis by gas cromatography. Rev.Colomb.Quim. [online]. 2012, vol.41, n.3, pp.377-394. ISSN 0120-2804.

The correct interpretation of a measurement result requires knowledge about its uncertainty. Very different approaches for the estimation of the uncertainty related to measurement results are found in the literature and in published guidelines. In this work two different approaches for uncertainty estimation are compared on an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits by gas chromatography with nitrogenous phosphorous detector. It was determined the contributions to the uncertainty at each analytical step such as extraction, clean up, evaporation and instrumental analysis. The first method was based on the guide to the expression of uncertainty in measurement (GUM) approach, which derives the uncertainty of a measurement result by combining the uncertainties related to the uncertainty sources of the measurement process. The second method was an approach previously presented by Haslòva and Stêpán, which included some elements of "top-down" estimation in that it included repeatability data generated by fortification experiments at different stages of the method to estimate the contribution of each step to the overall uncertainty. The results showed that when is employing GUM approach the uncertainty values were lowest compared with Haslòva method. Using the GUM approach uncertainty of standard preparation (uncertainties of weighing and diluting standards, uncertainties of purity of standards) was shown to represent the main source of combined standard. On the other hand, when the second method was used, the main source of uncertainty extraction process was identified. By contrast, it was found that the source contributes less to global uncertainty was the standards preparation. Finally, the expanded uncertainties for Haslòva method using a coverage factor of two were between 12.7% and 27.1% of the concentration, which was estimated uncertainty.

Keywords : pesticides; QuEChERS; uncertainty; gaschromatography.

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