Analysis Of Triglycerides In Edible Oils By Fourier Transform Ion Cyclotron Resonance Mass Spectrometric

Edible oil,mainly consisting of triglycerides,are crucial constituents in human life.At present,adulteration and counterfeit of edible oils have been reported frequently,and it has affected the health of human being.The problems are especially noticeable.It is important that analysis triglycerides in edible oils.In this paper,the analysis of triglycerides in edible oil was studied,which provided the conditions for the identification of adulterated oil.Two kinds of different ionization methods of matrix assisted laser desorption ionization mass spectrometry(MALDI MS)and atmospheric pressure chemical ionization mass spectrometry(APCI MS)were adopted to analyze triglycerides in edible oil by Fourier Transform Ion Cyclotron Resonance Mass Spectrometric(FT ICR-MS).The paper includes two part:(1)Triglycerides in edible oil was analyzed by MALDI MS.Through study of the matrix,surfactant,nitrocelluose film(NC),solvents,laser energy and sample point method,the method for analysis of triglycerides was established.Samples were dissolved in acetone as 15mg/mL.DHB matrix was prepared as a 100mg/mL solution in acetone solution.Small volume solution of sample and matrix were mixed in a ratio of 1:1(v/v)and then 1 ?L mixed solution was applied directly to a stainless steel MALDI target coated with 2B pencil lead and allowed to evaporate.The intensity of MALDI-laser irradiation was selected as 40%.The laser spot diameter was 2000um.The reproducibility(RSD)was calculated from ten sets of data.The RSD of in-dot,dot-to-dot and inter-day for three kinds of corn oils were all less than 7%.Using this method,the samples of edible oil from different types and different factories were analyzed respectively.Vegetable oil,in which the molecular ion peaks of triglycerides were mainly m/z 919.77,can be distinguished from animal fat,in which the molecular ion peaks of triglycerides were mainly m/z 897.80.The ratio of the abundances of m/z 897.80 to m/z 919.77(I897/I919)was observed in the mass spectra.The adulteration of 10%lard or mutton fat in corn oil was recognized directly.The sample of swill oil was analyzed.The swill oil is mixture of vegetable oil and animal fat.The structure of triglycerides in corn oil,soybean oil and lard were identified by secondary mass spectrometry(MS/MS).The mainly fatty acids were Stearic acid(S),Oleic acid(O),Linoleic acid(L),Linolenic acid(Ln).Palmitic acid(P)and so on.(2)Triglycerides in edible oil was analyzed by APCI MS.The effects on experimental factors were investigated,such as solvent,additives,corona needle,vaporizer temperature,flow rate,etc.Finally,experimental conditions were selected.Liquid samples of edible oil dissolved in acetonitrile to 1 ?L/mL,and solid samples dissolved in acetonitrile to about 0.8 mg/mL.Then,formic acid(1/‰)was pipetted onto liquid sample and solid sample respectively.Corona needle was 5000nA,vaporizer temperature was 250?,flow rate was set to 800?L/h.The RSD was calculated from five sets of data.The RSD of intra-day and inter-day for three kinds of corn oils were all no more than 5%.Using this method,the different kinds and different manufacturers of edible oils were analyzed.The results were consistent with the analysis of MALDI MS.The ratio of the abundances of m/z 857.89 to m/z 881.81(I857/I881)was observed in the mass spectra of APCI MS.The adulteration of 5%lard in corn oil was recognized directly.At the same time,the structure of triglycerides in corn oil,soybean oil and lard respectively were analyzed by MS/MS.The mainly fatty acids were Stearic acid(S),Oleic acid(O),Linoleic acid(L),Linolenic acid(Ln),Palmitic acid(P)and so on.Triglycerides of edible oil in the simulation of frying process were studied,in which some ester exchange reaction may be occured.The samples of swill oil and frying oil were analyzed.The swill oil is mixture of vegetable oil and animal fat,while frying oil is different from commercial edible oil.