Food Research Division, Bureau of Chemical Safety, Health Products and Food Branch, Health Canada, Ottawa, Ontario, Canada.
Anal Bioanal Chem. 2012 Jul;403(10):2933-42. doi: 10.1007/s00216-012-5932-8. Epub 2012 Mar 30.
An improved method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the analysis of glycidyl fatty acid esters in oils was developed. The method incorporates stable isotope dilution analysis (SIDA) for quantifying the five target analytes: glycidyl esters of palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2) and linolenic acid (C18:3). For the analysis, 10 mg sample of edible oil or fat is dissolved in acetone, spiked with deuterium labelled analogs of glycidyl esters and purified by a two-step chromatography on C18 and normal silica solid phase extraction (SPE) cartridges using methanol and 5% ethyl acetate in hexane, respectively. If the concentration of analytes is expected to be below 0.5 mg/kg, 0.5 g sample of oil is pre-concentrated first using a silica column. The dried final extract is re-dissolved in 250 μL of a mixture of methanol/isopropanol (1:1, v/v), 15 μL is injected on the analytical C18 LC column and analytes are eluted with 100% methanol. Detection of target glycidyl fatty acid esters is accomplished by LC-MS/MS using positive ion atmospheric pressure chemical ionization operating in Multiple Reaction Monitoring mode monitoring 2 ion transitions for each analyte. The method was tested on replicates of a virgin olive oil which was free of glycidyl esters. The method detection limit was calculated to be in the range of 70-150 μg/kg for each analyte using 10 mg sample and 1-3 μg/kg using 0.5 g sample of oil. Average recoveries of 5 glycidyl esters spiked at 10, 1 and 0.1 mg/kg were in the range 84% to 108%. The major advantage of our method is use of SIDA for all analytes using commercially available internal standards and detection limits that are lower by a factor of 5-10 from published methods when 0.5 g sample of oil is used. Additionally, MS/MS mass chromatograms offer greater specificity than liquid chromatography-mass spectrometry operated in selected ion monitoring mode. The method will be applied to the survey of glycidyl fatty acid esters in food products on the Canadian market.
建立了一种基于液相色谱-串联质谱（LC-MS/MS）分析油中缩水甘油脂肪酸酯的改良方法。该方法采用稳定同位素稀释分析（SIDA）定量分析 5 种目标分析物：棕榈酸（C16:0）、硬脂酸（C18:0）、油酸（C18:1）、亚油酸（C18:2）和亚麻酸（C18:3）的缩水甘油酯。对于分析，将 10mg 食用油脂或脂肪样品溶解在丙酮中，用氘标记的缩水甘油酯类似物进行标记，然后用 C18 和正相硅胶固相萃取（SPE）小柱进行两步色谱分离，分别用甲醇和 5%乙腈在正己烷中洗脱。如果分析物的浓度预计低于 0.5mg/kg，则先用硅胶柱对 0.5g 油样进行预浓缩。干燥后的最终提取物用 250μL 甲醇/异丙醇（1:1，v/v）重新溶解，取 15μL 注入分析用 C18 LC 柱，用 100%甲醇洗脱分析物。通过正离子大气压化学电离 LC-MS/MS 检测目标缩水甘油脂肪酸酯，采用多反应监测模式监测每个分析物的 2 个离子跃迁。该方法在不含缩水甘油酯的特级初榨橄榄油的重复样品上进行了测试。使用 10mg 样品，每个分析物的方法检测限范围为 70-150μg/kg，使用 0.5g 油样，方法检测限范围为 1-3μg/kg。10、1 和 0.1mg/kg 5 种缩水甘油酯的平均加标回收率范围为 84%-108%。本方法的主要优点是所有分析物均采用市售内标和 SIDA 进行定量分析，与使用 0.5g 油样时已发表方法相比，检测限降低了 5-10 倍。此外，MS/MS 质谱色谱图比在选择离子监测模式下运行的液相色谱-质谱具有更高的特异性。该方法将应用于加拿大市场食品中缩水甘油脂肪酸酯的调查。
