Regioisomeric Structure Determination of α- and γ-Linolenoyldilinoleoylglycerol in Blackcurrant Seed Oil by Silver Ion High-Performance Liquid Chromatography and Mass Spectrometry

Abstract

Gamma-linolenic acid (Gla) and oils containing Gla have evident positive effects on a variety of disorders, and therefore, the structure of triacylglycerols (TAGs) containing Gla is of special interest. The regioisomeric structures of TAGs 18:3(n-3)/18:2/18:2 (Ala/L/L) and 18:3(n-6)/18:2/18:2 (Gla/L/L) in blackcurrant seed oil were determined by Ag-HPLC/APCI-MS and Ag-HPLC/ESI-MS/MS techniques. In the latter, silver ion adducts were prepared by adding silver nitrate to the postcolumn flow. A new Ag-HPLC solvent system containing nonchlorinated solvents for the separation of Gla- and Ala-containing TAGs is introduced. Ag-HPLC separation of Ala/L/L and Gla/L/L was sufficient and regioisomers sn-LnLL + sn-LLLn and sn-LLnL (Ln, linolenic acid) could be differentiated well with the MS methods used. No discrimination was made between the sn-1 and sn-3 positions. The results show that the methods used are suitable to discriminate and determine the regioisomeric structure of TAGs. The regioisomeric structure of TAG with the fatty acid combination Gla/L/L in blackcurrant seed oil was considered to be practically random (32.7-37.8% of sn-LGlaL). In the fatty acid combination Ala/L/L, the regioisomeric structure is nonrandom (7.3-12.1% of sn-LAlaL) with Ala preferentially in a primary position. It can be concluded that the positional distribution of Ala and Gla is different in Ln/L/L TAGs of blackcurrant seed oil.

Regioisomer characterization of triacylglycerols by non‐aqueous reversed‐phase liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a postcolumn reagent

“…Laasko et al [15] found that the abundance of ions formed by the loss of a fatty acyl residue from the sn-2 position was less than that formed by a loss of fatty acyl residue from the sn-1/sn-3 glycerol position when APCI mass spectroscopy was used. Similar results were reported by Mottram et al [16] and Fauconnot et al [19] and also by Leskinen et al [13] when ESI source was used. Contradictory results were published concerning the identification of regioisomers using APCI: Segall et al [20] showed that analysis of sodium adduct molecular ions did not provide differences in the relative abundance of regioisomeric TAGs ions.…”

“…[11,12] Liquid chromatography-mass spectrometry (LC-MS) was also used in order to determine the regioisomery order of fatty acids in TAGs. Leskinen et al [13,14] determined the regioisomeric structure of some TAGs by Ag-HPLC-LC-MS-MS. However, inconsistent results were published as some of the authors could identify the positional isomers, whereas other demonstrated that no significant differences were observed between isomers.…”

Ozone-induced dissociation on a modified tandem linear ion-trap: Observations of different reactivity for isomeric lipids

“…Such sn-positional isomers are difficult to distinguish by mass spectrometry and thus structures are often reported as a single isomer based on assumptions about commonly occurring motifs (e.g., in glycerophospholipids unsaturated radyls are often assigned to the sn-2 position). Such unequivocal assignments are made despite the fact that numerous studies employing either selective enzymes or chromatographic methods have shown that both glycerophospholipids and triacylglycerols often appear in biology as mixtures of sn-positional isomers [5][6][7][8][9]. Despite the recent interest in the involvement of trans-fatty acids in increasing the risk of several chronic human diseases, particularly coronary heart disease [10,11], there has been relatively little attention paid to the possibility of stereoisomerism in complex lipids.…”

Regiospecific analysis of TAGs using chromatography, MS, and chromatography‐MS

“…Leskinen et al [24] studied the regioisomers of a-and glinolenoyldilinoleoylglycerol (AlaLL and GlaLL) in black currant seed oil by silver ion HPLC with APCI and ESI-MS-MS spectrometry. The silver ions were bonded to the ion exchanger column according to the procedure of Christie [3].…”