Analysis of alternaria metabolites by high-pressure liquid chromatography

A high-pressure liquid chromatogrphic (HPLC) method is described for analysis of Alternaria metabolites in grain sorghum and in cultures of Altenaria on grains. The metabolites were extracted from the sample with methanol in a blender. Ammonium sulfate solution was added to a portion of the methanol extract, and the resulting adqueous phase was partitioned first with hexane to remove oil and pigments and then with methylene chloride to extract the metabolites. A small silica gel column was usually used to clean extracts further. Metabolites were separated with Corasil II or Zorbax-SIL columns by either isooctane-tetrahydrofuran (THF) or petroleum ether-THF, with solvent programming, and detected by simultaneous monitoring of fluorescence and 350-nm absorbance. Quantitation of alternariol monomethyl ether, alternariol, and altenuene was usually based on fluorescence; less than 100 ppb of each compound could be detected. Other metabolites are mentioned briefly.