Challenges in Producing Reference Materials Used for Multi-Class Residue Testing in Food

Abstract

Monitoring contaminants, such as mycotoxin, pesticide, and veterinary drug residues, is crucial for ensuring food safety and protecting public health. Regular testing helps prevent harmful substances from entering the food supply, supports regulatory compliance, and ensures that food is safe for consumption. However, several analytical challenges are associated with residue analysis, including the need to monitor many measurands and matrix combinations, the ability to analyze multiple analyte forms, metabolites, and degradation products, and the need to detect residues at trace levels. To improve efficiency, there has been a trend of developing mass spectrometric-based, multi-class residue methods to analyze samples. Hundreds of analytes can be monitored using a single method for some of these multi-class methods. Method validation of these multi-class methods can be challenging due to the large number of measurands and matrices. Matrix reference materials (RMs) are extremely valuable when validating methods. However, this task is challenging for national metrology institutes (NMIs) and RM producers. It is not feasible to produce an RM with hundreds of measurands, and hence, it is necessary to prioritize residues and matrices. The use of RMs with incurred or endogenous analytes is preferable over spiked materials in that they can test the total extractability of a method. However, obtaining the quantities of incurred material that would be needed to produce an RM can be difficult. Furthermore, there could be long-term stability issues with some residues. The National Institute of Standards and Technology (NIST) has produced a few RMs to support residue testing in food. Standard Reference Material (SRM) 1565 Mycotoxins in Corn was designed to contain various mycotoxin classes (by blending several sources of incurred samples together) to support the development and validation of mass spectrometry-based methods capable of detecting multiple mycotoxins simultaneously. Currently, another mycotoxin RM is under development to support mycotoxin analysis in distiller’s dried grains with solubles, which is used as animal feed and can be a difficult matrix to analyze. NIST is examining the feasibility of producing small-batch research-grade test materials of food matrices with pesticide residues. One example is a prototype material consisting of ten pesticide residues in spinach, which was sent out in an interlaboratory study to determine community measurement capability and receive feedback on the material. Another small set of research-grade test materials was produced to compare two pesticide residues in two tomato materials, one incurred and one spiked. These studies may help make decisions on how to make fit-for-purpose RMs to support residue analysis. While some progress is being made in developing RMs to support multi-class residue methods, more work is needed. To further help the residue testing community, it is important to establish collaboration and communication between NMIs and RM producers, get feedback from stakeholders, and use other measurement services, such as interlaboratory studies, to help prioritize measurands and matrices.