RESUMEN
Limits of quantitation (LOQs) for a quadrupole ion storage tandem-in-time mass spectrometry (QISTMS) method were evaluated through replicate analysis of unfortified peanut oil, shortening, lamb fat, and butter for all 2,3,7,8-chlorine-substituted polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs). Ten congeners were measurable in butter (0.27-2.5 pg/g) and nine congeners were measurable in lamb fat (0.09-2.6 pg/g) with good precision. LOQs for high-fat foods were estimated by triplicate analysis of peanut oil fortified at two levels. Accurate and reproducible results were achieved at 0.5 pg/g for most PCDD/Fs (1.0 pg/g for heptachlorodibenzo-p-dioxin and heptachlorodibenzofuran and 2.0 pg/g for octachlorodibenzofuran) and at 0.2 pg/g for 2,3,7,8-tetrachlorodibenzofuran (TCDF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). QISTMS distinguished between catfish and chicken eggs with elevated TCDD levels from background samples collected from the most regions of the continental United States. QISTMS determined the extent of TCDD contamination in butter, lamb fat, and cottonseed oil collected from rural villages in Kazakhstan. Replicate analysis of catfish and chicken eggs by the QISTMS method produced comparable results to high-resolution mass spectrometry (HRMS). Lower limits of detection will be needed if QISTMS is to fully complement HRMS in the measurement of TCDD levels in food.