Simultaneous multiple mycotoxin quantification in feed samples using three isotopically labeled internal standards applied for isotopic dilution and data normalization through ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry.

RATIONALE: Mycotoxins are typically present in grain and are also concentrated in distillers dried grains with solubles (DDGS), common feed ingredients for food animals. The diversity of mycotoxins and feed matrices has made the routine detection and quantification of mycotoxins in feed both complex and prohibitively expensive. METHODS: Ultra-performance liquid chromatography/electrospray ionization triple quadrupole detection (UPLC/ESI-TQD) (tandem mass spectrometry, MS/MS) with (13) C-labeled isotopic dilution was used to analyze internal standard isotopologues of three mycotoxin molecules, as well as 29 other structurally differing mycotoxin molecules from four common feed matrices: corn, wheat, barley, or DDGS. Mycotoxins were extracted via a single-step procedure using a mixture of acetonitrile/water/formic acid. Labeled isotopologues were used as a surrogate to account for extraction quality and as internal standards for the evaluation of the feed matrix signal suppression/enhancement (SSE) contributed by each mycotoxin and by each matrix. The SSE was corrected by matrix-matched calibration with blank certified reference feed material. RESULTS: The limits of detection for individual mycotoxins in buffer ranged from 0.01 to 206.7 µg/mL but could increase by up to four times depending on the matrix effect. The accuracy and precision were enhanced by the use of isotopically labeled standards. The recoveries were somewhat negatively affected by the SSE contributed by each matrix. Each mycotoxin was successfully detected and assigned to one of four SSE categories: high (-66%), intermediate (-48%), low (-19%) signal suppression and signal enhancement (> +300%). CONCLUSIONS: An improved LC/MS method was validated, which offers a practical and economical means for large-scale detection and quantification of multiple mycotoxins in common animal-feed matrices, including DDGS.