Reversed-phase thin-layer chromatography of diacylglycerols as their labile dimethylborate esters

Silver ion liquid-chromatographic mobility of plant diacylglycerols as a function of their composition and spatial arrangement

Coordination complexes of unsaturated rac-1,2-diacylglycerols (DAGs) with silver ions were separated by adsorption and reversed-phase TLC (silver ion TLC and silver ion RP-TLC, respectively). During silver ion TLC, silver ion complexes are formed by an indeterminate number of coordination centers of various nature and only at the adsorbent surface; separation of the complexes proceeds according to an adsorption mechanism, and there is an inverse exponential relationship between DAG unsaturation and their mobility. With silver ion RP-TLC, the complexes are formed only with double bonds, only in solution, and at a 1:1 ratio; the complexes are fractionated by lipophilic partitioning between two liquid phases, and the relationship between the unsaturation of DAGs and their mobility is a direct linear one. Nevertheless, in spite of all these differences, the use of both methods demonstrated that DAG species characterized by a coiled acyl configuration always greatly exceeded in polarity those with the same unsaturation, but with the configuration close to an extended one; in the former group, this excess amounted to two- to three-fold and 30-40% for silver ion TLC and silver ion RP-TLC, respectively. In addition, for both versions of silver ion LC, these two groups of species differ from each other quantitatively, but not qualitatively, in the pattern of the relationship between the unsaturation and mobility of DAG complexes. Thus, under all conditions of silver ion LC studied here, the polarity of DAG complexes and, therefore, their mobility are conditional not only on the number of double bonds, but also on their configuration.

Silver ion chromatography of lipids and fatty acids

Silver ion chromatography as applied to the analysis of lipids is reviewed. Thin-layer, column, high-performance liquid and supercritical fluid chromatography in the silver ion mode are included. The lipid types covered are fatty acids, triacylglycerols and complex lipids. Separations are divided into those according to number, geometry and position of double bonds, as well as acyl positional isomers for triacylglycerols. The mechanism of silver ion chromatography is discussed in relation to recent studies using silver ion high-performance liquid chromatographic methodology.

Determination of neutral lipids from subcutaneous fat of cured ham by capillary gas chromatography and liquid chromatography

The determination of neutral lipids in fat of cured ham is reported. Fat samples were extracted with chloroform-methanol (2:1) and neutral lipids and free fatty acids were separated on an aminopropyl minicolumn, the first fraction with chloroform-2-propanol (neutral lipids) and the second fraction with 2% acetic acid in diethyl ether (free fatty acids). Neutral lipids were fractionated with minicolumns, with aminopropyl and silica stationary phases. Two fractions were obtained with the first column: (A) triglyceride and cholesteryl esters and (B) cholesterol and mono- and diglycerides. Fraction A was applied to the silica column to obtain two new fractions: (C) cholesteryl esters and (D) triglycerides. Fractions B and C were analysed by capillary gas chromatography (cGC) and fraction D by cGC and HPLC. The R.S.D.s obtained were below 5% except for the monoglycerides (8%). Cholesteryl esters were determined by cGC in 5 min with R.S.D. 5%. The main triglycerides identified were PPO, POS, POO, POL and OOO (P = palmitic acid, O = oleic acid, L = linoleic acid; S = stearic). Monoglyceride and diglycerides having 18, 34 and 36 carbon atoms were the most abundant. The determination of triglycerides by HPLC was more difficult than by cGC because the linearity with HPLC was concentration dependent. The procedure allowed the determination of neutral lipid classes without derivatization of mono- and diglycerides.