Comparability of measurement results for pesticide residues in foodstuffs: an open issue?

Abstract

The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way of ensuring comparability of measurements in this field.