The reliability of residue data strongly depends on the quality of sample homogenization prior to analysis. While in the last decade the sensitivity of instruments has strongly improved and was intensively discussed, information on the crucial step of sample homogenization is very limited in public literature. Yet, high quality of sample homogenization is needed, as for example, Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration (Sanco/10058/2005) requires a low degree of data scatter in order to obtain high significant degradation parameters. Therefore, we conducted a homogenization study for which we chose soil as the matrix. We modified a food processing machine so that it could with stand the strong exerted forces during homogenization. In the experimental design, we considered several influencing factors: (1) soil type (clay loam and sandy loam), (2) polarity of the pesticide (polar and non-polar), (3) type of sample (soil core and grab sample), and (4) sample size (600 g to 8 kg). Soil samples were spiked with 0.2 mg/kg pesticide, homogenized, and 5 g aliquots of each sample were analyzed. Factors influencing the homogenization quality could be distinguished by high replicate field sample analysis. Soil type and sample size influenced sample homogenization most, while other factors were of less importance. Homogenization was optimized by modification of scissor setup and processing duration. Our data show that such optimization of the homogenization technique is crucial and significantly improves representativeness of analytical results. However, even with the high effort taken, the variation of residue values after homogenization was always higher than the analytical error.

Optimization of sample homogenization for pesticide residue analysis: Soil � an example for a difficult matrix

246th National Meeting (2013)

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