Some recent advances in the chromatographic analysis of lipids

Abstract

Procedures for structural analysis of fatty acids and high-performance liquid chromatographic (silver ion, adsorption, reversed-phase and chiral) analysis of lipids are in the forefront of developments. Supercritical-fluid chromatography is making a lesser impact.A ny selection of the most interesting and va l u abl e a dvances in the ch ro m at ographic analysis of lipids over the last few ye a rs must be a subjective one, conditioned by the ex p e rience of the author. With this caveat, I suggest that procedures for structural analysis of fatty acids must be high on any list, and those involving gas chromatography-mass spectrometry in particular. Similarly, m e t h o d o l ogy involving high-perfo rmance liquid ch ro m at ography (HPLC) has been developing apace, especially in the area of silver ion chromatography, lipid class analysis and molecular species analysis. The increasing use of evaporative light-scattering detection has greatly assisted with the last. With such instruments, the mobile phase coming from the end of the HPLC column is evaporated in a stream of air in a heated chamber; the solute does not evaporate, but is nebulized and carried as minute droplets through a light beam, which is reflected and refracted. The amount of scattered light is measured by a photomultiplier tube and bears a relationship to the concentration of material eluted from the column. In that they will respond to any lipid that does not evaporate before passing through the light beam, such There has also been a great deal of interest in the application of supercritical-fluid chromatography to the analysis of lipids. However, in my opinion, there is still little that can be done by this technique that is not better accomplished by GC or HPLC. A comprehensive r eview of this methodology has also appeared [2]. Structural analysis of fatty acidsThe potential of mass spectrometry for identification of fatty acids of natural origin has been evident for many years, but there were few reports of structural analyses on real samples as opposed to model compounds until re l at ive ly re c e n t ly. The problem has been largely solved by the use of specific amide or ester derivatives, which following ionization in the mass spectrometer stabilize the charge on a nitrogen atom remote from the structural features of interest. Radical-induced cleavage predominates in the aliphatic chain and distinctive fragmentations are achieved according to the position of double bonds, b ra n ch-points or ring stru c t u res. In p a rt i c u l a r, the use fi rst of py rro l i d e, and subsequently of picolinyl ester or 2-alkenyl-4,4-dimethyloxazoline (DMOX) derivatives, of fatty acids permits GC-MS to be employed for the separation and characterisation of these compounds from natural lipids. The technique has been aided by the ava i l ability of improved cap i l l a ry columns. Indeed, s u ch derivatives only began to be used widely when GC columns of fused silica became available, although initially it was only possible to use non-polar stationary ph...

Structures, practical sources (gymnosperm seeds), gas-liquid chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cis Δ5-olefinic acids

“…The structure of 5,9,12,15-octadecatetraenoic (coniferonic) acid has also been confirmed as the DMOX derivative [6], as has that of 5,11,14,17-eicosatetraenoic (juniperonic) acid [57,86].…”

Arachidonic, eicosapentaenoic, and biosynthetically related fatty acids in the seed lipids from a primitive gymnosperm, Agathis robusta

“…It can be seen that it differs appreciably from that of arachidonate and of eicosapentaenoate. In particular, gaps of 26 amu between m/z = 260 and 286, 300 and 326, and 340 and 366 define the double bonds in positions 11, 14, and 17, respectively; the fact that the ion at m/z = 151 is of low abundance and the presence of distinctive ions at m/z = 219 and 232 are characteristic of an isolated double bond in position 5 (76). Spectra for the DMOX derivatives of fatty acids with double bonds in position 5 have been described by Berdeaux and Wolff (29).…”

Multidimensional Liquid Chromatography Coupled with Tandem Mass Spectrometry for Identification of Bioactive Fatty Acyl Derivatives

“…Silver ion, or argenation, chromatography has been used extensively for separation of lipid samples with a high variation of unsaturation numbers and geometrical configuration, such as are commonly found in triacylglycerols (Dobson et al, 1995; Christie, 1998a,b; Momchilova et al, 1998; Nikolova-Damyanova et al, 2003; Adlof, 2004, 2007; Dugo et al, 2004, 2006a,b; Mondello et al, 2005; Christie et al, 2007). The general mechanism of action in this separation scheme is unclear, though Christie and co-workers propose a theory of silver ions forming weak, reversible charge transfer complexes with the analytes (Dobson et al, 1995; Christie, 1998c; Momchilova and Nikolova-Damyanova, 2003; Nikolova-Damyanova, 2009).…”