非正常食用油的在线甲基化-气相色谱测定及模式识别分析研究

On-line methylation-gas chromatographic determination with pattern recognition analysis for illegal cooking oils

建立了食用油中脂肪酸组成的在线水解甲基化-气相色谱测定方法,分析了20余种常用食用油与非正常食用油样品。将1μL(3 mg/mL)油脂样品与2μL衍生化试剂四甲基氢氧化铵(TMAH,25%甲醇溶液)加入裂解器,在350℃下,油脂加水分解瞬间衍生化成相应的脂肪酸甲酯。基于气相色谱图上分离鉴定到的10个共有峰的相对强度,建立了食用油的气相色谱指纹图谱。结合化学模式识别即主成分分析和系统聚类分析对合格食用油和非正常食用油样品的色谱图进行了识别分析。结果表明,建立的指纹图谱结合模式识别技术可以较好的区分合格食用油与非正常食用油样品。

A method of on-line hydrolysis and methylation-gas chromatography（OHM-GC） was developed for the determination of composition of fatty acids in the cooking oils.More than 20 cooking oil samples and illegal cooking oil samples were analyzed by OHM-GC using a vertical microfurance pyrolyzer.1 μL of（3 mg/mL） oil sample and 2 μL of organic alkali,tetramethylammonium hydroxide（TMAH,25% methanol solution） taken in a sample cup was first mounted at the waiting position of the pyrolyzer kept at around room temperature,then it was dropped into the heated center of the pyrolyzer under the flow of helium carrier gas.Thermally assisted hydrolysis and methylation of the samples at 350 ℃ in the presence of TMAH allowed analysis of fatty acids as their corresponding methyl derivatives,and the products formed were introduced into a gas chromatograph equipped with a flame ionization detector or mass spectrometer.Based on the relative peak areas of 10 peaks in the chromatogram obtained by OHM-GC,the samples were clearly classified by principle component analysis and hierarchical cluster analysis.The fingerprints developed showed a high similarity and a good reproducibility,and the pattern recognition techniques can distinguish illegal oils from cooking oils well.The results proved that it was a simple,rapid and accurate method,which was suitable for the discrimination of illegal oils.