New approach via gene knockout and single-step chemical reaction for the synthesis of isotopically labeled fusarin c as an internal standard for the analysis of this fusarium mycotoxin in food and feed samples.

The gold standard for quantitation of contaminants with high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) is the use of isotopically labeled standards. Herein, we report a new strategy for the synthesis of isotopically labeled 21-d3-fusarin C via a genetically modified Fusarium strain, followed by a one-step derivatization reaction. Fusarin C is a Fusarium mycotoxin, which is mutagenic after metabolic activation. Its occurrence has been demonstrated recently in corn-based samples, but up to now, little is known about the contamination of other grain samples. To collect further data, the quantitation method was enhanced by application of the 21-d3-fusarin C and the use of a QTRAP 5500 mass spectrometer. This new method has a limit of detection (LOD) of 1 μg/kg, a limit of quantitation (LOQ) of 4 μg/kg, and a recovery rate of 99%. A total of 21 corn samples and 13 grain samples were analyzed, with resulting fusarin C levels varying from not detectable to 24.7 μg/kg.