Acetonitrile Chemical Ionization Tandem Mass Spectrometry To Locate Double Bonds in Polyunsaturated Fatty Acid Methyl Esters

Abstract

A rapid method is presented for determining the location of double bonds in polyunsaturated fatty acid methyl esters (FAME) using an ion-trap mass spectrometer. The mass spectrum of the chemical ionization reagent acetonitrile in an ion trap includes a m/z 54 ion, identified previously as 1-methyleneimino-1-ethenylium ion. We show that it reacts with double bonds of polyunsaturated FAME to yield a series of covalent product ions all appearing at (M + 54)+. Collisional dissociation of these ions yields diagnostic fragments, permitting unambiguous localization of double bonds. For methylene-interrupted and conjugated FAME, one of these fragments results from loss of the hydrocarbon end of the chain, while the other involves loss of the methyl ester. Major diagnostic-fragment ions for monoene and diene FAME occur as a result of cleavage adjacent to either allylic sites or double bonds in the original analyte and appear at one mass unit above the mass expected for homolytic cleavage. Fragmentation of polyene FAME yields major diagnostic ions resulting from cleavage between double bonds that appear one mass unit lower. The method is shown to produce highly characteristic spectra for FAME with 1 to 6 double bonds. Identification of double-bond position in highly unsaturated fatty acids is demonstrated in a mixture of unknown polyunsaturated FAME from an extract of cultured Y79 human retinoblastoma cells.

Investigation and Applications of In-Source Oxidation in Liquid Sampling-Atmospheric Pressure Afterglow Microplasma Ionization (LS-APAG) Source

“…Analytical approaches for rapidly acquiring their structure information (e.g., chain lengths, the degree of unsaturation, and double bond positions) is highly desirable as their functions are closely related to molecular structures. Current analytical approaches primarily rely on MS, which has been emerging as a useful tool with the advent of some special dissociation methods (e.g., charge-remote fragmentation [38] and ozone-induced dissociation [39]) and the introduction of off-line/on-line chemical modifications, such as alkylthiolation [40], olefin cross-metathesis [41], Paternò-Büchi reaction [42], acetonitrile chemical ionization (CI) [43,44], and oxidative cleavage by strong oxidants. Among them, oxidative cleavage is easily available via a series of oxidants.…”

The polypyrimidine tract binding protein regulates desaturase alternative splicing and PUFA composition

“…FAME were analyzed in triplicate and quantifi ed by gas chromatographyfl ame ionization detection (GC-FID), using an equal weight FAME standard mixture to verify response factors daily ( 29 ). Peak identities were confi rmed by GC-covalent adduct chemical ionization tandem mass spectrometry (GC-CACI-MS/MS) (30)(31)(32). The standard deviation for ratios (fold change in treated/control) was calculated using a propagation-of-error approach.…”

The Influence of Moderate and High Dietary Long Chain Polyunsaturated Fatty Acids (LCPUFA) on Baboon Neonate Tissue Fatty Acids

“…Fatty acid methyl esters (FAME) were prepared using sodium hydroxide and 14% boron-trifluoride (BF 3 ) in methanol, and were analyzed by gas chromatography (HP 5890; BPX-70 column, SGE, Austin, TX), using H 2 carrier gas as described previously (17). FA identities were determined by covalent adduct chemical ionization tandem mass spectrometry (19) and then quantified using methyl heptadecanoate as an internal standard and response factors derived from an equal weight FAME mixture. FA concentrations are expressed as percentage weight of total FA from 14 to 24 carbons.…”