The Study Of A Novel Method Based On Derivatization Technique For Ms Analysis Of Free Fatty Acids And Its Applications

Free fatty acid(FFA)or nonestesterified fatty acid(NEFA),is the decomposition product of lipids such as triacylglycerols,phospholipid and glycolipid.Free fatty acids(FFAs)generated from the hydrolysis of triacylglycerols(TAGs)in oils during manufacturing process and storage,are easily led to the oxidation and rancidity of oil,impairing oil quality and functionality.Therefore,FFA content is one of the most concerned indexes to characterize high-quality oils and to evaluate oil damage.The FFA content is also a parameter that may be used to control the oil degradation produced by storage under different conditions of moisture,temperature,oxygen,and light and to follow the thermal degradation of the oils used to cook or fry,which is very useful in specific applications,such as determining the need to replace frying fats.The traditional measuring methods of FFA in edible oil are titration method for the determination of acid value and gas chromatography(GC).The sensitivity of titrating method is insufficient for catering to the wide range of edible oil quality and only total FFAs in fats and oils can be determined,but the variety of FFA and its content still remain unclear.Although GC can provide the qualitative and quantitative information of free fatty acids in edible oils,a complicated sample extraction and purification process and FFA methyl ester derivatization are required before GC analysis because of the relatively low concentration of FFAs with strong polarity and weak volatile in a highly complex matrix of oil.The whole process is very complex,cumbersome,time consuming and requires a lot of organic solvent,in addition,the poor stability and low detection sensitivity prevent GC from the most reliable method.Therefore,it is very necessary to establish a highly efficient,selectively and sensitive qualitative and quantitative analysis method for free fatty acids.This project focuses on the development of a novel method for high selective and sensitive qualitative and quantitative analysis of free fatty acids through integrating chemical derivatization technique with electrospray ionization tandem mass spectrometry(ESI-MS/MS),and solving the technical bottlenecks of existing MS technologies on free fatty acids analysis.The major results of the paper are as follows:1.A strategy based on simple chemical derivatization coupled with ESI-MS/MS for rapid and sensitive detection of FFAs was developed.After N,N-diethyl-1,2-ethanediamine(DEEA)derivatization,the detection sensitivity of FFAs was increased about 2200~6700-fold with the neutral loss scan-shotgun electrospray ionization tandem-quadrupole mass spectrometry analysis(NLS-Shotgun ESI-MS/MS).With mass spectrometry neutral loss scanning mode combined with the internal standard quantitative analysis,the rapid determined analysis of free fatty acids has been realized,and it provided a novel strategy of thinking to solve the problems of mass spectrometry low ionization efficiency and poor sensitivity in FFAs analysis2.In order to verify the feasibility of the established method for FFA analysis,the developed method was applied to quantitative analysis of FFAs in edible oils,and comparing the analysis results measured by Gas chromatography-flame ionization detection(GC-FID)and High performance liquid chromatography couple with mass spectrometry(HPLC-MS),respectively.By using this method,oil samples can be simply diluted by n-hexane,derivated with DEEA,and then directly infused and analyzed by shotgun-ESI-MS/MS without complicated sample purification treatments.3.The established method was applied to determine dynamic FFA formation in seven types of edible oils subjected to a microwave heating treatment test.Eight FFAs were detected in edible oils,and FFA contents of C18:1,C18:2 and C18:3 increased after microwave treatment.4.The developed method was applied to determine dynamic FFA formation in rapeseed samples from eight different sources after microwave heating processing.8 FFAs in rapeseed samples were determined.After microwave heating treatment,FFA contents in the cold drawn oil from rapeseed samples increased generally.Principal component analysis(PCA)demonstrated that the FFA contents varied among these eight rapeseed samples.This approach is simple,practical and reliable,the changes of FFAs contents would be monitored to ensure the safety and quality of edible oil.It offers a potential application for edible oil authenticity control and adulteration detection.