Determination of Fatty Acid Methyl Esters by Gas Chromatography-Flame Ionization Detection: Response Mechanism and Quantitative Pattern

In light of the shortcomings of the quantitative methods for the determination of fatty acid methyl esters (FAME) using gas chromatography-flame ionization detection (GC-FID) specified by the current Chinese and international standards, this work systematically studied the response pattern, theoretical model, and experimental interfering factors in the GC-FID method for the determination of 37 FAME through theoretical derivation and laboratory validation from the perspectives of instruments, chromatographic columns, split ratio, and standard substances. Then, the concepts of “quality coefficient” and “correlation factor” were proposed to reveal the functional relationship and equivalence conditions between experimental relevance factors (FF_E) and theoretical relevance factors (FF_T). Through multiple experiments, the stability of the correlation factors was confirmed. It was found that the theoretical quality coefficient (QC_T) and the FF_T could be fully utilized for relative or absolute quantification of FAME with more than 10 carbon atoms. The experimental quality coefficient (QC_E) and FF_E for FAME with less than 10 carbon atoms could be accurately measured through methods such as freshly preparing FAME reference materials and be used to correct the amount of FAME for quantitative analysis. This not only improved the accuracy of quantitative results, but also increased the timeliness of the use of reference materials and reduced the amount of reference materials used.