Preparation of a reference material for tea containing five pesticide residues and its evaluation in an interlaboratory comparison study in China

Monitoring pesticide residues is a key item in the field of food safety. Tea matrices represent a challenge in pesticide analysis due to the high content of coextracts. An interlaboratory comparison was organized to assess the performance of 73 laboratories, from 28 regions in China, on the quantification of five pesticide residues in tea matrix reference material in order to ensure the accuracy, reliability and comparability of monitored pesticide residues in foods. The tea matrix reference material spiked with pesticides was prepared according to ISO 17034. Briefly, blank green tea was spiked with bifenthrin, permethrin, fenpropathrin, buprofezin and imidacloprid, smashed, sieved, homogenized and bottled. It was assessed to be sufficiently homogeneous and stable. Participant laboratories were requested to submit quantification results with detailed analytical protocols. Assigned values were obtained from consensus values by robust analysis, and the results were assessed using z scores. The robust standard deviations for five pesticides were lower than the expected standard deviations in our interlaboratory comparison. In total, 93.8 % (255/272) of the results were acceptable (|z|≤ 2.0) and 82.2 % (60/73) of participant laboratories had satisfactory performance in pesticide residues quantification. Analytical protocols of extraction, cleanup and quantification methods were reviewed to assess their impacts on the results. Overall, a tea matrix reference material was successfully prepared for an interlaboratory comparison, and the results indicate that most of domestic laboratories have acceptable capability in pesticides quantification, while a few of them need to further optimize their protocols to improve performance.