Preparation of a Lyophilized Bovine Milk Reference Material for Quality Control of Amoxicillin Detection

A bovine milk reference material was produced containing amoxicillin with a target concentration at the maximum residue limit. For the evaluation and characterization of the reference material, an isotope dilution-liquid chromatography/tandem mass spectrometry method was developed and validated. This material was prepared by collecting milk samples from cows treated with an appropriate amoxicillin injection, followed by freeze-drying, dilution, and homogenization of the authentic samples. The amoxicillin reference material, prepared in accordance with ISO Guide 35, was homogeneous and stable. It was assigned a certified value of (4.10 ± 0.13) μg/kg with a relative standard deviation between 2.93 and 5.29%, which meets the maximum residue limit (MRL) requirement of 4.0 μg/kg established by the United States, the European Union, and China. This reference material can be used for method validation and provides internal quality control assurance for the detection of amoxicillin.