Triglycerides chromatograph

Oils are mixtures of mixed esters with different fatty acids distributed among the ester molecules. Generally, identification of specific esters is not attempted instead the oils are characterized by analysis of the fatty acid composition (8,9). The principal methods have been gas—Hquid and high performance Hquid chromatographic separation of the methyl esters of the fatty acids obtained by transesterification of the oils. Mass spectrometry and nmr are used to identify the individual esters. It has been reported that the free fatty acids obtained by hydrolysis can be separated with equal accuracy by high performance Hquid chromatography (10). A review of the identification and deterrnination of the various mixed triglycerides is available (11). 

Margarine is an example of a solid sample where the materials of interest are soluble in one solvent (in this case methanol) whereas the matrix materials, largely triglycerides, are not. As a consequence, the sample preparation procedure is relatively simple. The chromatographic separation is achieved by using the dispersive interactions between the hydrocarbon chains of the fatty acids and the hydrocarbon chains of a reversed phase. 

Figure 39, A lipid pattern from normal serum which has been scanned for density of the thin-layer chromatograph, showing the various peaks, P, phospholipids C, cholesterol F, free fatty acids S, internal standard, T, triglycerides CE, cholesterol esters.

Nova-Pak C18 column in a methanol water chloroform gradient.92 Choline chloride was added to the mobile phase. One review of techniques used in the analysis of triacylglycerols lists over 300 references on separations of the triglyceride fraction of fats using nonaqueous RPLC, aqueous RPLC, argen-tation chromatography, and other chromatographic methods.93... 

The elution factors in normal-phase TLC and RP-HPLC, using a fixed set of chromatographic parameters, were determined for a series of saturated triacylglycerides with TCN from C30 to Ceo, serving as reference compounds and various oxidation derivatives of analogous unsaturated triglycerides, including hydroperoxides, peroxides, epoxides, core aldehydes and their DNP derivatives. From these measurements, a series of incremental... 

In order to determine the fatty acid composition of the triglycerides, they have to be first hydrolysed and the liberated fatty acids converted to their methyl esters, which have a good chromatographic peak shape compared to the free acids. A convenient method for achieving hydrolysis and methylation in one step is shown in Figure 11.8. 

Gas chromatographic methods for the qualitative analysis of complex systems such as biological materials and bacteria, proteins, steroids and prostaglandins, and triglycerides have been developed. 

Silica columns can tolerate relatively heavy loads of triglyceride and other nonpolar material. Such material is not strongly adsorbed and can easily be washed from the column with 25% diethyl ether in hexane after a series of analyses (83). Procedures for determining vitamins A and E have been devised in which the total lipid fraction of the food sample is extracted with a non-aqueous solvent, and any polar material that might be present is removed. An aliquot of the nonpolar lipid extract containing these vitamins is then injected into the liquid chromatograph without further purification. Direct injection of the lipid extract is possible because the lipoidal material is dissolved in a nonpolar solvent that is compatible with the predominantly nonpolar mobile phase. Procedures based on this technique are rapid and simple, because there is no need to saponify the sample. 

Firestone, D. (1994) Liquid chromatographic method for determination of triglycerides in vegetable oils in terms of their partition numbers summary of collaborative study. J. AOAC Int., 77, 954—957. 

Fincke, A. (1980) Possibilities and limits of gas chromatographic triglyceride analyses for detection of extraneous fats in cocoa butter and chocolate fats. II. Distribution of triglycerides classified by C number in cocoa butter substitutes and other fats. Deut. Lebensm.-Rundsch., 76(6), 187-192. 

Geeraert, E. and de Schepper, D. (1983) Structure elucidation of triglycerides by chromatographic techniques. Part 2 RP HPLC of triglycerides and brominated triglycerides. J. High Res. Chromatogr., 6, 123-132. 

Robinson, J.L. and Macrae, R. (1984) Comparison of detection systems for the high-performance liquid chromatographic analysis of complex triglyceride mixtures. J. Chromatogr., 303, 386-390. 

Lercker, G., Frega, N., Bocci, F. and Bertacco, G. (1992) Milk fat. Gas chromatographic analysis of triglycerides in assessment of authenticity of butter. Scienza Tecnica Lattiero Casearia, 43, 95-110. 

Najera, A.I., Perea, S., Barcina, Y., de Renobales, M. and Barron, LJ.R. (1999) A reverse-phase high performance liquid chromatographic method for analyzing complex mixtures of triglycerides. Application to the fat fraction of an aged cheese. J. Am. Oil Chem. Soc., 76, 399-407. 

Saeed, T., Ali, S.G., Abdul-Rahman, H.A. and Sawaya, W.N. (1989) Detection of pork and lard as adulterants in processed meat liquid chromatographic analysis of derivatized triglycerides. J. Assoc. Off. Anal. Chem., 12, 921-925. 

Schneller, R. and Wullschleger, R. (1992) Quantitative determination of milk fat in fat mixtures by gas chromatographic analysis of triglycerides. Mitt. Gebiete Lebensm. Hyg., 83, 737-744. 

European Commission. 1999. Reference method for the detection of foreign fats in milk fat by gas chromatographic analysis of triglycerides - revision 1. Commission Regulation (EC) No 2771/1999 Annex II. Official Journal of the European Communities L 333/23. 

Precht, D., Frede, E. 1994. Determination of the solid fat content in milk fat by gas chromatographic triglyceride analysis. Fett IViss. Technol., 96, 324-330. 

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