Study on production of reference material for plant protection chemicals: bifenthrin, carbofuran, chlorpyrifos, difenoconazole, imidacloprid in milk powder matrix

Controlling pesticide residues in food is a top concern to ensure consumer health and safety. In testing, reference materials (RM) and certified reference materials (CRM) are essential tools used to calibrate equipment, control quality and confirm the reliability of analytical methods. This study focuses on the production, storage and evaluation of certified reference materials of five pesticides: bifenthrin, carbofuran, chlorpyrifos, difenoconazole, imidacloprid in powdered milk, in compliance with international standards ISO 17034:2016 and ISO 33405:2024. The RM after production and packaging were analyzed by gas chromatography (GC) (for bifenthrin and chlorpyrifos) and liquid chromatography (LC) (for carbofuran, difenoconazole and imidacloprid) using tandem mass spectrometry detector (MS/MS) to evaluate homogeneity, stability and estimate shelf life. The results showed that at room temperature, the RM was estimated to be stable with all five pesticides for at least 2 years. The RM after evaluation was used to successfully organize a proficiency testing program with the participation of 07 testing laboratories nationwide. The certified value is accompanied by the expanded measurement uncertainty of each pesticide: difenoconazole 77.90 ± 10.35 µg/kg; carbofuran 81.55 ± 10.02 µg/kg; bifenthrin 68.38 ± 8.47 µg/kg; imidacloprid 65.15 ± 8.22 µg/kg; chlorpyrifos 69.04 ± 13.97 µg/kg.