Rapid determination of double bond configuration and position along the hydrocarbon chain in cyclic fatty acid monomers

Abstract

This study reports the structural elucidation of diunsaturated 5- or 6-membered ring cyclic fatty acid monomers (CFAM) isolated from heated flaxseed oil by complementary gas chromatography (GC)-mass spectrometry (MS) and GC-matrix isolation-Fourier transform infrared spectroscopy (MI-FTIR). Infrared measurements of CFAM were carried out on methyl ester derivatives as well-resolved chromatograms were obtained on a polar 100% cyanopropyl polysiloxane capillary GC column. By contrast, electron ionization MS of methyl ester derivatives was of limited value because of double bond migration during the ionization process in the mass spectrometer. This communication reports definitive MS fragmentation patterns that can confirm ring position and double bond position along the fatty acid chain in 1,2-disubstituted CFAM determined as 2-alkenyl-4,4-dimethyl-oxazoline derivatives. Double bond configuration (cis, trans, or conjugated cis,cis) in CFAM was confirmed by GC-MI-FTIR. The presence of CFAM, degradation products found in used frying oils, is a potential source of dietary toxicity.

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

“…Pyrrolidide, picolinyl, and dimethyl oxazoline derivatives [10], double-bond deuteration, silylation [11], and preparation of dimethyl disulfide adducts [12] are among the derivatization methods used for the determination of double-bond positions. While many studies have been made on the determination of the position of double bonds, there are very few reports on identification of the geometry of double bonds in fatty acids using mass spectrometry [9,[13][14][15][16][17][18][19][20][21]. These methods include fast atom bombardment (FAB) [13,19], collision induced MS of fatty acids cationized by copper [14], acetonitrile chemical ionization [15], resonance electron capture [16], electron impact ionization (EI) of picolinyl derivatives and chemometrics [17], EI of 2-alkenyl-4,4-dimethyl-oxazolin derivatives [18], and EI of Diels-Alder adducts using 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene [20,21].…”

Application of on-line capillary GC-FTIR spectroscopy to lipid analysis

“…Cell sizes are 10-20 cm by approximately 1 mm (i.d.). The relatively low sensitivity LP flow cells are less attractive than matrix isolation (MI) [5,6] or direct deposition (DD) GC-FTIR interfaces [2] which are more useful for lipid analysis [3,[7][8][9][10][11][12][13]. The minimum identifiable quantity for LP systems is in the range of 5-25 ng per analyte, but sensitivity may be improved by approximately an order of magnitude with the MI and DD interfaces.…”

“…GC-MI-FTIR spectroscopy was applied to the separation (on long highly polar capillary columns) and characterization of partially hydrogenated vegetable oil fatty acid methyl ester (FAME) components [3,[7][8][9][10][11][12][13]. Using FTIR as detector for GC, chromatographic traces were usually obtained by monitoring the carbonyl absorption at 1754 cm -1 .…”

“…The reportedly toxic cyclic fatty acid monomers (CFAMs) are readily absorbed by the digestive system [14]. Determination of the double bond configuration for a complex mixture of CFAMs isolated from heated flaxseed oil was achieved by GC-MI-FTIR for methyl ester and 2-alkenyl 4,4-dimethyl oxazoline (DMOX) derivatives [10][11][12][13].…”

The effects of cyclic fatty acid monomers on cultured porcine endothelial cells

“…A ring structure is formed within the same fatty acyl chain to create a CFAM molecule [Scheme 1 where x Because of their unique structure, the physical characterization of CFAM has been under investigation since their identification in heated oils and only recently have novel analytical techniques been applied to definitively confirm the structure of CFAM (22)(23)(24). The metabolic and physiologic effects of fatty acids and lipid oxidation products in tissue culture systems have been reported in the literature (25)(26)(27)(28)(29).…”