Development of Avocado Reference Material for Pesticide Residue Analysis

Background Pesticide quantitation in foods relies on the availability of matrix reference materials, which, however, are scarce because of the general instability of pesticides. In particular, no avocado reference material has been developed. Objective This research aimed to develop a reference material to support the determination of pesticide residues in avocado. Method Avocado was spiked with 11 selected pesticides at levels of 0.01-0.35 mg/kg. The production process included the assessment of between-unit heterogeneity, stability during dispatch, and best storage conditions according to ISO 17034. Reference values were estimated through an interlaboratory comparison study involving laboratories of demonstrated competence and adhering to ISO/IEC 17025. The corresponding expanded uncertainties were calculated as 4-19% in compliance with the Guide to the Expression of Uncertainty in Measurement. Results The reference material was sufficiently homogeneous and stable at 4 degrees C during the entire study period (365 days) for most of the pesticides, and at 40 degrees C during 10 days, but it was unstable at 50 and 60 degrees C during 10 days. Four pesticides showed downward trends; however, this behavior was considered in the uncertainty budget. As this material complied with all requirements of proficiency testing, it was used in an interlaboratory proficiency test designed to investigate analytical performance and assist laboratories in improving the quality of measurement results. Conclusions The presented material can be used for the development of novel analytical methods or in-house reference materials and adds to the scarce supply of reference materials for the determination of pesticides in vegetable matrixes with high oil contents and intermediate water contents.