植物油中甘油稳定碳同位素组成的测定

建立了气相色谱-燃烧-稳定同位素比值质谱(GC-C-IRMS)法结合酯交换技术测定植物油中甘油的稳定碳同位素组成(δ13 C)。样品溶于异辛烷后,在氢氧化钾-甲醇溶液中转化为甘油和脂肪酸甲酯,去除脂肪酸甲酯后用GC-C-IRMS法测定甘油的δ13 C。结果表明,食用油中甘油δ13 C的测定标准偏差为0.18‰,且酯交换过程不会导致甘油碳同位素分馏。通过分别测定玉米胚芽油、大豆油和玉米胚芽油与大豆油的混合植物油中甘油的δ13 C值,并进行结果比较,表明甘油δ13 C值与玉米胚芽油中大豆油的含量呈显著负相关(R2=0.98),可通过测定甘油δ13 C值验证大豆油掺入玉米胚芽油的比例。本方法前处理简单、测定结果准确,可用于食用油掺假的鉴定。

Determination of the Stable Carbon Isotopic Composition of Glycerol in Vegetable Oils

A method of gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS) with ester exchange technology was established for the determination stable carbon isotope composition (δ¹³C) of glycerol in vegetable oils. After the sample was dissolved in isooctane, triglyceride produces glycerol and fatty acid methyl ester under the existence of KOH methanol solution.δ¹³C of glycerol was determined by GC-C-IRMS after the removal of fatty acid methyl ester. Through the optimization of reaction time, the best time is 4 h after addition of KOH methanol solution. Results show that the standard deviation is 0.18‰, and the ester exchange process does not lead to glycerol carbon isotope fractionation. By analysing the differences ofδ¹³C value of glycerol in corn oil and soybean oil,δ¹³C values are -14.71‰ and -31.30‰, respectively,δ¹³C value of glycerol has a significant negative correlation (R²=0.98) with content of soybean oil in corn germ oil. The method has an advantage of easy and rapid operation, and which is applicable forδ¹³C analysis of adulteration of vegetable oil. This study provides a theoretical basis and technical support for the identification of varieties of vegetable oils.