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Submitted to: Encyclopedia of Mass Spectrometry
Publication Type: Other Publication Acceptance Date: 8/11/2005 Publication Date: 10/1/2006 Citation: Byrdwell, W.C. 2006. Analysis of triglycerides and related compounds in food using liquid chromatography/mass spectrometry techniques. Encyclopedia of Mass Spectrometry (M.L. Gross and R.M> Caprioli, Ed.), Elsevier B.V., p. 654-664. Interpretive Summary: Liquid chromatography combined with mass spectrometry has become a very popular technique for analysis of the complex mixture of components in vegetable oils. The primary components of dietary fats and oils are triacylglycerols (TAG), which contain three fatty acids (FA), which are long chains of carbons and hydrogens, attached to a three-carbon glycerol backbone. TAG can be made up of many different types of FA having different carbon chain lengths and different numbers of double bonds (unsaturation). Saturated fats, monounsatured fats, and polyunsaturated oils each have come from different animal or plant sources and have different effects on the body. The chapter “Analysis of Triglycerides and Related Compounds in Food Using Liquid Chromatography/ Mass Spectrometry Techniques” presents an introduction to fats and oils, and gives information to allow people interested in their analysis to decide what is the best technique to use for their analysis. The chapter describes what data looks like that comes from each type of mass spectrometry used, and how that data can be interpreted to understand more about the structures of fats or oils. Two techniques of liquid chromatography – mass spectrometry are discussed: atmospheric pressure chemical ionization (APCI) mass spectrometry and electrospray ionization (ESI) mass spectrometry. This article is written for new graduate students and for scientists from disciplines other than mass spectrometry who are interested but not yet well versed in the subject of mass spectrometry for analysis of triacylglycerols. Technical Abstract: The most common ionization sources available today to couple liquid chromatography (LC) with mass spectrometry (MS) are atmospheric pressure ionization (API) sources that form ions at ambient pressure and sample them into the high vacuum region of the mass analyzer. The two most popular API sources are atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). These techniques have been used extensively for LC-MS analysis of lipids. Triacylglycerols (or triglycerides) are large non-polar lipid molecules that constitute the fats and oils consumed in the diet. These contain three fatty acid (FA) chains attached to the three carbon backbone of a glycerol molecule. LC-MS can be used to characterize TAG based on the lengths of the FA chains, the number of double bonds in the FA, and sometimes the positions of the double bonds. LC-MS can also be used to identify the regiospecificity of the FA, which is their location on the glycerol backbone. APCI-MS and ESI-MS provide complementary information from TAG. APCI produces a gentle fragmentation that provides detailed structural information. ESI-MS requires an ionic additive, or reagent, to form ions, and produces primarily intact adduct ions, which provide molecular weight information. These adducts may be used as precursor ions which are fragmented using collision-induced dissociation (CID) to form structurally informative fragment ions. ESI-MS/MS produces mass spectra that appear very similar to those given by the gentle in-source fragmentation of APCI. These two techniques will be discussed and compared for their suitability for analysis of triglycerides using liquid chromatography-mass spectrometry. |
