Laboratory Performance Assessment via Interlaboratory Comparison on Analysis of Quat Herbicides in Potatoes

Interlaboratory Comparison of Herbicides Testing

Abstract

        Quat compounds, including paraquat, diquat, chlormequat, and mepiquat, are widely used as non-specific herbicides. The residue analysis of these substances in food must be controlled by competent laboratories. In 2025, the Bureau of Quality and Safety of Food conducted an interlaboratory comparison (ILC) for the analysis of quat herbicides in potatoes. The objective was to assess the analytical performance of both government and private laboratories for the determination of quat herbicides in fruits and vegetables. For the ILC sample preparation, potato blank samples were procured and fortified with two standards, including paraquat and chlormequat. The homogenized samples were divided into two sets (test sample 1 and test sample 2), and each set was spiked with different standard concentrations. Homogeneity tests were performed before distribution to participating laboratories. The interlaboratory comparison results were evaluated using statistical methods based on ISO 13528:2022. The assigned value for paraquat was determined following the consensus value of the participants, while the value for chlormequat originated from a single laboratory result. The standard deviation for interlaboratory comparison assessment was calculated using Horwitz's equation modified by Thompson. The ILC sample stability was studied under two storage conditions, including at ≤ -15ºC and at 2−8ºC for 3 days. The results revealed that the ILC samples were adequately stable. The analytical results from 11 participating laboratories were assessed using z-scores or z'-scores to demonstrate the laboratories competence. Among the 14 results of paraquat and the 7 results of chlormequat, 92.9% and 85.7% were “acceptable”, respectively. The results indicate that the measurement capabilities in these laboratories can be considered mostly trustworthy and reliable.