Assessment of in-house reference materials for multi-pesticide residue analysis in three food matrices by LC-MS/MS: development, homogeneity, and stability.

In-house reference materials (ihRM) are an alternative to the limited supply of reference materials for method validation and assurance of the validity of pesticide residue results. Currently, limited information exists on producing ihRM of pesticide residues in food for laboratory testing purposes for the desired matrix/analyte/concentration combination. This study aimed to develop in-house reference materials for three food matrices: banana, rice, and green coffee spiked with a total of 22 pesticides, which were selected for their relevance in food matrices, with pK values ranging from -0.13 to 5.8 following the guidelines of ISO Guide 80:2014. In this study, we assessed the impact of spiking (solvent) and drying conditions (freeze-dried and oven) on homogeneity uncertainty. The final step of this work involved evaluating the homogeneity and kinetics for long-term stability (4 °C) according to the ISO 33405 guidelines, using a fully validated method based on QuEChERS and measurement by LC-MS/MS through a completely randomized block design with two-way ANOVA, and simple linear regression analysis for homogeneity and stability, respectively. In general, for the three matrices, it was found that using a predominantly aqueous solvent (>70%) and freeze-drying resulted in sufficient homogeneity and no significant processing trends (slope p-value > 0.05), compared to using an organic medium (>70%), which resulted in uncertainties up to 50 times higher for several analytes. On the other hand, uncertainties for long-term stability below 3% were obtained for most of the analytes at 4 °C. The results demonstrate that homogeneous and stable ihRMs can be obtained under the provided preparation conditions, although special attention is required for processing conditions, particularly for the banana at a larger scale.