Abstract
Reducing the analytical portion size during pesticide residue analysis can potentially reduce the amounts of organic solvents
and reagents used, as well as the time required for analysis. However, if sample processing is not performed properly and the
concentration distribution of the pesticide residues in the homogenized sample is not uniform, the analytical portion may not represent
the original sample, thereby leading to large variations in analytical values and incorrect results. In this study, we compared variations
in the analytical values of incurred residues in various vegetable and fruit portions of different size (2–20 g) in order to examine how
portion size affects the analytical values obtained during pesticide-residue analysis. The results show that variations in the analytical
values are relatively small (relative standard deviation < 10%) for foods that can form homogeneous samples relatively easily when
appropriate sample processing methods were employed, even when a 2-g analytical portion was used for analysis. In contrast, for
foods such as grapes that are not easily homogenized, large variations in the analytical values were observed for analytical portions
less than 5 g in size due to variations in the distributions of pesticide residues in the sample. Furthermore, to examine the effect of the
sample processing method on sample homogeneity, variations in the analytical values of incurred residues in tomato were compared
using three methods, namely sample processing at room temperature using a household food processor, laboratory-knife milling, and
cryogenic milling. Sample processing using a household food processor was found to provide large variations in the analytical values
(relative standard deviation > 20%), even when a 20-g portion was used for analysis. The results show that, compared to the other
two methods, sample processing at room temperature using a household food processor may not provide sufficiently homogeneous
samples.
