The contamination of food and feed by mycotoxins, Aflatoxin B (AfB) being one of the most prominent examples, is of imminent concern to many countries. Regulatory limits for mycotoxins have been implemented, and these need to be supported by a sound measurement infrastructure for mycotoxin analysis in order to enforce and verify products, protect populations, and avoid technical barriers to trade in food stuffs. A Capability Building and Knowledge Transfer program on Metrology for Safe Food and Feed in Developing Economies was started at the International Bureau of Weights and Measures to allow National Metrology Institutes or Designated Institutes to work together to strengthen their national mycotoxin metrology infrastructure. Knowledge transfer to scientists is provided to enable the characterization of selected pure mycotoxin materials and the production of corresponding certified reference material solutions. This higher-order measurement capability can in turn support mycotoxin testing laboratories within their countries through the provision, for example, of standard solutions of critical analytes that are traceable to the International System of Units (SI). The purity characterization and value assignment for a high-purity AfB material (979.6 ± 2.3 mg/g, = 2) intended to be used for the gravimetric production of SI traceable calibration solutions for AfB is described using an approach combining quantitative NMR and LC-diode array detection-tandem MS for the correction of the mycotoxin-related impurity content.