Contribution of Sample Processing to Variability and Accuracy of the Results of Pesticide Residue Analysis in Plant Commodities

Abstract

Significant reduction of concentration of some pesticide residues and substantial increase of the uncertainty of the results derived from the homogenization of sample materials have been reported in scientific papers long ago. Nevertheless, performance of methods is frequently evaluated on the basis of only recovery tests, which exclude sample processing. We studied the effect of sample processing on accuracy and uncertainty of the measured residue values with lettuce, tomato, and maize grain samples applying mixtures of selected pesticides. The results indicate that the method is simple and robust and applicable in any pesticide residue laboratory. The analytes remaining in the final extract are influenced by their physical-chemical properties, the nature of the sample material, the temperature of comminution of sample, and the mass of test portion extracted. Consequently, validation protocols should include testing the effect of sample processing, and the performance of the complete method should be regularly checked within internal quality control.

Assessment of Test Portion Sizes after Sample Comminution with Liquid Nitrogen in an Improved High-Throughput Method for Analysis of Pesticide Residues in Fruits and Vegetables

“…Recently, a series of articles have been published in an attempt to change that oversight among analytical chemists in the pesticide residue analysis community. [1][2][3][4][5][6][7][8][9][10] Regulatory purposes require that bulk commodities typically >1 kg be collected and processed to yield pesticide determinations that accurately correspond to the original sample lot (e.g. shipment or warehouse).…”

“…Despite its importance as a significant source of error, the comminution step, including the taking of test portions, is rarely included in analytical method validation or routine quality control (QC) protocols. Recently, a series of articles have been published in an attempt to change that oversight among analytical chemists in the pesticide residue analysis community. − …”

“…Defenders of the status quo may say that the comminution steps have already been validated, but previous studies actually show that quality of sample processing is highly dependent upon techniques, devices, analytes, and matrices, often contributing >50% to the overall measurement uncertainty in real-world analysis. ,,− ,, By that logic, proficiency testing is unnecessary because analytical methods in common use have already been extensively validated by many analysts in many laboratories worldwide, including via frequent proficiency testing analyses for decades. , However, very few validation studies of sample processing have been conducted by comparison. Despite this reality, regulators and analytical chemists continue to ignore the comminution step in proficiency testing, method validation, and routine QC practices.…”

Influences of sample homogenization time and standing time before extraction on the determination of incurred pesticide residue levels in grapes

“…[1][2][3][4][5][6] It is also necessary to prepare an adequate sample homogenate with fine particles to reduce the uncertainty induced by errors in weighing the extract portions analyzed and to ensure sufficient extraction efficiency for pesticide residues in the samples. [6][7][8][9][10] It is necessary to weigh extract portions from a sample homogenate without a bias in content between the peel and pulp portions of fruits, because the majority of pesticide residues from foliage ap-plication with short pre-harvest intervals are present in the peels of fruits such as melons. 11) Similarly, it is necessary to prepare a sample homogenate without a bias in content between the outer and inner leaves of wrapped leafy vegetables such as cabbage, because the majority of pesticide residues from foliage application are present in the outer leaves.…”

“…Grapes were selected from among the worst-case samples because they have hard and thin skins and soft pulp portions, like tomatoes. 6,8) In this homogeneity test, we investigated the distribution of pesticide residues in the sample homogenate in combination with different conditions, such as blending time, standing time after blending, and the use of hand mixing for frozen-thawed samples.…”