C-13 internal standards for mycotoxins analysis: trend or necessity?

Mycotoxins are fungal secondary metabolites, occurring in a wide spectrum of food and feed commodities worldwide. They may exert acute and chronic adverse effects on humans and animals.

In consideration of the typical mycotoxin co-occurrence in crops and their extensive combination in food, co-exposure to multiple mycotoxins through one’s diet should be considered for a proper risk assessment. A regulatory framework is currently enforced in many parts of the world, although still not harmonised at a global level. In the European Union, according to the farm-to-fork precautionary approach, the maximum permitted levels are particularly low, reaching sub-part per billion in the case of the most dangerous aflatoxins (eg, 0.05 μg/kg for aflatoxin M1).

Owing to the efforts of the agro-food system to meet regulatory compliance, the accuracy and reliability of analytical methods used in the industry and in official labs must be the highest possible, to avoid both false positive and false negative results.

Over the last 20 years, mass spectrometry has become the benchmark in food analysis for a large range of contaminants and, more recently, multi-analyte methods have been established as the golden standard for many classes of chemicals. However, analysts working with mass spectrometry are well aware of the possible matrix effect, due to ion suppression or ion enhancement, that may influence accurate quantification.

In the case of multiple analytes occurring at trace level in a complex food matrix, the choice of internal standard (ISTD) is crucial to minimise possible bias in quantification. The most effective strategy to ensure proper accuracy is Isotope Dilution Mass Spectrometry (IDMS). This approach is based on the use of stable isotope labelled standards, human‑made compounds that cannot occur in naturally contaminated samples and are able to compensate for possible losses and matrix effects occurring during the analysis.^1,2

Regarding mycotoxin analysis, all the regulated compounds are available on the market as C-13 standards, meaning that all the carbon atoms in the molecules are substituted by 13C atoms.