Abstract
Fatty acids (FAs) are the central components of life: they constitute biological membranes in the form of lipid, act as signaling molecules, and are used as energy sources. FAs are classified according to their chain lengths and the number and position of carbon–carbon double bond, and their physiological character is largely defined by these structural properties. Determination of the precise structural properties is crucial for characterizing FAs, but pinpointing the exact position of carbon–carbon double bond in FA molecules is challenging. Herein, a new analytical method is reported for determining the double bond position of mono- and poly-unsaturated FAs using liquid chromatography-mass spectrometry (LC–MS) coupled with solvent plasmatization. With the aid of plasma on ESI capillary, epoxidation or peroxidation of carbon–carbon double bond in FAs is facilitated. Subsequently, molecular fragmentation occurs at or beside the epoxidized or peroxidized double bond via collision-induced dissociation (CID), and the position of the double bond is elucidated. In this method, FAs are separated by LC, modified by plasma, fragmented via CID, and detected using a time-of-flight mass spectrometer in a seamless manner such that the FA composition in a mixture can be determined. Our method enables thorough characterization of FA species by distinguishing multiple isomers, and therefore can uncover the true diversity of FAs for their application in food, health, and medical sciences.
Highlights
Fatty acids (FAs) are the central components of living organisms as they are structural components of phospholipids and sphingolipids that constitute biological membranes, can be converted into physiologically active signal molecules, and serve as energy sources[1,2,3,4,5]
We previously reported a method for analyzing a range of FA species in biological samples in a single assay by using reverse-phase LC–MS12,27, where FAs were distinguished by their chain lengths and number of double bonds
Zhao et al reported that epoxidation of unsaturated FAs by lowtemperature plasma and subsequent fragmentation using Electrospray ionization (ESI)–MS can determine the position of carbon–carbon double bond[15]
Summary
Fatty acids (FAs) are the central components of living organisms as they are structural components of phospholipids and sphingolipids that constitute biological membranes, can be converted into physiologically active signal molecules (i.e. eicosanoids and lysophospholipids), and serve as energy sources[1,2,3,4,5] Their chemical characteristics are primarily determined by their carbon chain length as well as the number and position of carbon–carbon double bonds. Derivatization with N-(4-aminomethylphenyl)pyridinium (AMPP) at the terminal carboxy group provides the informative fragment ions for carbon–carbon double bond[25,26] With these methods one can deduce the exact position of the carbon–carbon double bond of unsaturated FAs. We previously reported a method for analyzing a range of FA species in biological samples in a single assay by using reverse-phase LC–MS12,27, where FAs were distinguished by their chain lengths and number of double bonds. In combination with our previous method, the current method enables full characterization of a FA species and thorough profiling of the FA composition in biological samples or in food resources
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