Confirmation of identity of aflatoxins

Aflatoxins are detected and determined by analytical procedures based on physical and chemical properties, e.g., ultraviolet absorbance, fluorescence, solubility and Chromatographie retention times during thin layer (TLC) or liquid chromatography. For acceptance of analytical results based on these properties, especially for regulatory purposes, proof of identity of the compound being measured is essential. Numerous tests have been devised for confirmation of identity. Included are tests based on toxicological effects observed in the duckling, zebrafish, chick embryo, Bacillus megaterium and many other species; chemical tests based on formation of derivatives such as the acetates and water adducts; and tests based on color changes of TLC spots after contact with spray reagents, e.g., sulfuric acid. All of the foregoing have inherent uncertainties in interpretation of identity. On the other hand, mass spectrometry (MS) is one of the most specific methods of identification available; however, it has been difficult to apply at the low concentrations at which aflatoxins are routinely detected. In this paper, the confirmation techniques for aflatoxins are placed in historical perspective and are reviewed and evaluated A recently developed procedure for the application of negative ionization MS for the confirmation of identity of aflatoxins in foods or feeds at concentrations as low as 10 ng/g is described. This procedure consists of isolation of the aflatoxin by Association of Official Analytical Chemists’ methods, purification by preparatory 2‐dimensional TLC, in situ elution of the aflatoxin TLC spot and analysis of the sample by negative ion chemical ionization MS using a direct insertion probe.