Determination of mycotoxins in milk-based products and infant formula using stable isotope dilution assay and liquid chromatography tandem mass spectrometry.
A stable isotope dilution assay and liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and validated for the determination of 12 mycotoxins, aflatoxins B?, B?, G?, G?, and M?, deoxynivalenol, fumonisins B?, B?, and B?, ochratoxin A, T-2 toxin, and zearalenone, in milk-based infant formula and foods. Samples were fortified with 12 ¹³C uniformly labeled mycotoxins ([¹³C]-mycotoxins) that correspond to the 12 target mycotoxins and prepared by dilution and filtration, followed by LC-MS/MS analysis. Quantitation was achieved using the relative response factors of [¹³C]-mycotoxins and target mycotoxins. The average recoveries in fortified milk, milk-based infant formula, milk powder, and baby yogurt of aflatoxins B?, B?, G?, and G? (2, 10, and 50 ?g/kg), aflatoxin M? (0.5, 2.5, and 12.5 ?g/kg), deoxynivalenol, fumonisins B?, B?, and B? (40, 200, and 1000 ?g/kg), ochratoxin A, T-2 toxin, and zearalenone (20, 100, and 500 ?g/kg), range from 89 to 126% with RSDs of <20%. The individual recoveries in the four fortified matrices range from 72% (fumonisin B?, 20 ?g/kg, milk-based infant formula) to 136% (T-2 toxin, 20 ?g/kg, milk powder), with RSDs ranging from 2 to 25%. The limits of quantitation (LOQs) were from 0.01 ?g/kg (aflatoxin M?) to 2 (fumonisin B?) ?g/kg. Aflatoxin M? was detected in two European Reference materials at 0.127 ± 0.013 ?g/kg (certified value = 0.111 ± 0.018 ?g/kg) and 0.46 ± 0.04 ?g/kg (certified value = 0.44 ± 0.06 ?g/kg), respectively. In 60 local market samples, aflatoxins B? (1.14 ± 0.10 ?g/kg) and B? (0.20 ± 0.03 ?g/kg) were detected in one milk powder sample. Aflatoxin M? was detected in three imported samples (condensed milk, milk-based infant formula, and table cream), ranging from 0.10 to 0.40 ?g/kg. The validated method provides sufficient selectivity, sensitivity, accuracy, and reproducibility to screen for aflatoxin M? at nanograms per kilogram concentrations and other mycotoxins, without using standard addition or matrix-matched calibration to compensate for matrix effects.