Liquid chromatographic determination of tenuazonic acids in tomato paste

Abstract

Tenuazonic acid is a mycotoxin produced by Alternaria alternata (A. tenuis) occurring in isolates from tomato. Several liquid chromatographic (LC) systems were compared for suitability in analyzing tomato pastes for tenuazonic acid. Tenuazonic acid was extracted from tomato paste with methanol and n-hexane and was partitioned into methylene chloride from the aqueous methanol following acidification. It was further partitioned into 5% NaHCO3, acidified, and reextracted with methylene chloride. LC separation of tenuazonic acid from interferences was best on a C12-dien (4-dodecyldiethylenetriamine) loaded C18 reverse phase column with a mobile phase containing C12-dien, Zn(II), and ammonium acetate, or on a tetraalkylammonium anion exchange column at pH 7.5. Two isomeric tenuazonic acids could be partially separated in the C12-dien/metal system using acetonitrile in the mobile phase. Amounts of standard tenuazonic acid as low as 2-5 nm. Recoveries of tenuazonic acid or isotenuazonic acid added to tomato paste at levels of 0.4-10 micrograms/g were 67-94%. Small amounts of tenuazonic acid were detected in several commercial tomato pastes at levels of 0.01-0.1 micrograms/g. Gas liquid chromatography/mass spectrometric (GLC/MS) single ion monitoring showed that both isomers were present.