Preparative gas-liquid chromatography of lipids

Applications of preparative gas-liquid chromatography of lipids are presented and discussed. Various designs of preparative units are reviewed, including those commercially available. A general discussion of preparative gas-liquid chromatography is presented with emphasis on the practical problems involved.     

Quantitative gas-liquid chromatography of triglycerides

To determine optimum operating conditions, an extensive study was made of the variables affecting quantitative recovery and resolution of model triglyceride mixtures. Parameters investigated included: flash heater temperature, carrier gas flow rate, type of carrier gas, column length, glass and metal columns, temperature program rate, linearity of detector response, physical design of gas chromatograph, and molecular species of triglyceride. Results indicate that with optimum operating conditions, triglyceride molecular weights through trierucin can be quantitatively analyzed. Accurate calibration is essential, since quantitative response factors vary somewhat with operating conditions, triglyceride carbon number, and the chromatograph used. Cocoa butter and rat adipose tissue triglycerides have been quantitatively analyzed by this technique. Presented at the AOCS meeting in Houston, Texas, 1965.     

Identification of peaks in gas-liquid chromatography

Some of the known principles of gas-liquid chromatography are reviewed. Application of the equivalent chain length (ECL) method to identification of complex molecules, and to prediction of structures of unknowns, is described in detail. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

An electrostatic precipitator for preparative gas-liquid chromatography

The effect of the operating variables of electrostatic precipitators on the recovery and structure of methyl esters and related aerosol forming compounds collected in preparative gas-liquid chromatography was studied. Aerosol formation was prevented by AC or DC voltages of 5000 to 12000 volts. AC was more effective than DC but caused changes in structure which were detectable by both thin-layer and gas-liquid chromatographic methods of analysis. An apparatus of simple construction and operation was designed for the collection of methyl esters and its use demonstrated with several model compounds.     

Determination of cyclic fatty acids by gas-liquid chromatography

A method is described to determine cyclic fatty acids in cyclic monomers by gas-liquid chromatography (GLC), which separates saturated straight-chain esters from cyclic esters. The content of cyclic esters can be determined by integration of the area on the chromatograph under the cyclic peaks. GLC was applied to cyclic monomers made from linseed oil and from linolenic acid. Samples of both hydrogenated and nonhydrogenated cyclic monomers were analyzed; however, more reliable results were obtained on the hydrogenated samples. The results show a standard deviation of 0.25 for linseed oil and 0.36 for linolenic acid. Accuracy of the analysis was established by comparing data with that obtained by crystallization. The GLC method is approximately three times faster. Presented at the AOCS meeting, New Orleans, La., 1962. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

The determination of hydrophile-lipophile balance by gas-liquid chromatography

Measurement of the relative retention time of a pair of liquids, one polar and one nonpolar, permits determination of the polarity of the liquid Chromatographic substrate. It is shown that this polarity is a measure of the hydrophile-lipophile balance (HLB) when the substrate is a surface-active agent. The effects of structure, additivity in mixtures, and free polyol are discussed. A GLC apparatus, designed, to permit the rapid determination of HLB by this technique, is described.     

Characterization of unsaturated fatty acids by gas-liquid chromatography

The equivalent chain length (ECL) has been determined on 79 methyl esters of unsaturated fatty acids and on 7 ethyl esters by gas chromatography. Ethylene glycol succinate (EGS), diethylene glycol succinate, β-cyclodextrin acetate and Apiezon L were chosen as the liquid phases to be used. For methyl esters of mono- and polyenoic acids, the differences between ECL on EGS and ECL on Apiezon L approximate 0.84 per double bond. For positional isomers, the ECL on both EGS and Apiezon L are usually greater for the isomer having the longer proximal end of the molecule (smallest ω value). In these terms a triple bond is approximately equal to three double bonds. Esters of nonconjugated dienoic and trienoic acids of the same chain length are not separable on Apiezon L if their proximal structures are the same. This also applies to tetraenoic and pentaenoic acids of the same chain length and the same proximal structure. Conjugation of double bonds, either with the ester carbonyl group or with themselves, yields ECL values on Apiezon L greater than the number of carbon atoms in the acid. Monounsaturated and nonconjugated polyunsaturated esters have ECL values on Apiezon L lower than the number of carbon atoms of the acid. The ECL values of ethyl esters of 18 and 20 carbon acids are greater than the corresponding methyl esters on Apiezon L. Presented at the Chicago meeting of the American Oil Chemists’ Society, Oct. 13, 1964.     

Identification and estimation of tocopherols by gas-liquid chromatography

A gas chromatographic method is described for the identification and estimation of the individual tocopherols as their trimethylsilyl (TMS) ethers. The TMS ethers are prepared by dissolving the sample in a mixture of hexamethyl-disilazane, trimethylchlorosilane, and anhydrous pyridine (2:1:10), and allowing it to stand for at least 15 min. The separations described were made at 235C on 0.08 in. I.D. ×15 ft silanized glass columns packed with either 0.5% Apiezon L or 2% SE-30 on 110/120 mesh Anakrom (acid and base washed, and silanized). Retention data, obtained either by chromatographing known compounds or by prediction using the Kováts Retention Indices, are presented for tocol, tocotrienol, and all 14 possible methylated tocols and tocotrienols. The quantitative results from the analyses of two standard mixtures are also presented. The application to naturally occurring tocopherols is illustrated by chromatograms of partially purified fractions from soy oil, wheat germ oil, whole wheat flour, and corn meal.     

Separation of organic mixtures by sequential gas-liquid chromatography

A new sequential continuous chromatographic refiner (SCCR-2) for high temperature production scale G.L.C. (gas-liquid chromatographic) separations is described. In this equipment the counter-current movement between the gas and liquid phase is simulated by sequencing a system of inlet and outlet port functions around twelve static 2.54 cm internal diameter and 61 cm long stainless steel columns. The versatility of the equipment has been demonstrated by the separation of equivolume mixtures of the halocarbons arklone P/genklene P, methylchloroacetate/ethyl lactate and ethyl caprate/ethyl laurate at temperatures of 60°, 105° and 160°C respectively. Throughputs between 21–75 cm³h^?1 have been explored with product purities in excess of 99.8% achieved under certain process conditions.     

Suitability of lipid extraction procedures for gas-liquid chromatography

A comparison of two methods of extracting liver tissue lipids has been made using a limited amount of experimental material. The extracts prepared by a procedure using Bloor’s reagent were more stable in storage, contained nearly 100% more total lipids and phospholipids, and produced more uniform and reproducible patterns on gas chromatographic analysis, than extracts of the same liver prepared by a diethyl ether Soxhlet extraction. Presented in part at the AOCS meeting in New Orleans, La., 1962.     

Fatty acid composition of rice lipids by gas-liquid chromatography

Gas-liquid Chromatographic analysis of the methyl ester of lipids of four rice varieties showed that bran lipids had significantly higher mean contents of linoleic and linolenic acids, but lower contents of myristic, palmitic, palmitoleic, and stearic acids than milled rice lipids. Nine fatty acids were detected. The principal components were oleic, linoleic, and palmitic, which also was confirmed by thin-layer chromatography of the esters. Issued as I.R.R.I. Journal Series No. 12     

A study of asphalt-aggregate interactions using inverse gas-liquid chromatography

Aggregate surfaces were shown to interact strongly with many i.g.l.c. test compounds having chemical functional groups similar to those believed present in asphalt.

1 Asphalt refers to the binder in road mixes. In many countries the binder is referred to as bitumen.

I.g.l.c. and infra-red spectroscopy showed that fractions in the asphalt containing the more polar functional groups exhibited the stronger interaction with the aggregate surface. Asphaltenes separated by pentane show a reduced interaction of polar groups with the aggregate, probably because of agglomeration of the asphaltene molecules. Oxidation of the asphalt fractions produced polar functional groups which interacted strongly with aggregate surfaces. Aggregate surfaces were found to catalyse the oxidation of the more non-polar fractions. Their catalytic effect on the more polar fractions is unknown. Of the two aggregates tested, limestone was found to interact more strongly than quartzite with the asphalt fractions, although quartzite was a more effective oxidation catalyst for the more non-polar fractions. Carboxylic acids were found to be a major component formed on oxidation that is strongly adsorbed on the limestone surface.     

Application of gas-liquid chromatography to the study of gas-bitumen interactions

Gas-liquid chromatography (glc) has been used (Xu and Hepler, 1990) to obtain Henry's Law constants and infinite dilution activity coefficients for hydrocarbon and other vapour-phase solutes in two bitumens, Athabasca and Wolf Lake. Thermodynamic interaction between components widely different in molar mass can, however, be characterized by mass-fraction rather than mole-fraction based quantities and by the χ parameter, as has been the practice with polymer systems. The new parameters have been calculated and reveal more unfavorable interactions of the solutes with Wolf Lake than with the Athabasca material.     

The analysis ofCis-trans fatty acid isomers using gas-liquid chromatography

The geometric isomers of many unsaturated fatty acid methyl esters can be separated using high-resolution gas-liquid chromatography on polyester or Apiezon columns. Separations reported for the geometric isomers of monounsaturated, ricinoleic, linoleic, conjugated, and epoxy fatty acids are reviewed here. New data is presented on the resolution of linolenate geometric isomers on both polyester and Apiezon columns. The separation of methyl oleate and methyl elaidate on a polyester column has also been accomplished. Techniques for preparing and using the high-resolution columns necessary for these separations are reviewed. Presented at the AOCS meeting in New Orleans, La., 1962. Supported in part by a grant from the National Institutes of Health (A-6011).     

Quantitative fatty acid analysis of vegetable oils by gas-liquid chromatography

Summary The fatty acid composition of a number of vegetable oils and of two synthetic mixtures of methyl esters are compared by gas-liquid chromatography and by standard methods. The calculated iodine values from G.L.P.C. results are in good agreement with measured iodine values and are indicative of the reliability of the G.L.P.C. values. Standard methods gave lower values for linoleic acid and higher values for linolenic acid than did G.L.P.C. This deviation was particularly evident in oils with a high proportion of linolenic acid,e.g., linseed oil. The results of G.L.P.C. are considered to be accurate to within one unit percentage. Thermal stability of the polyester polymers can be improved by using 1,4-butanediol or ethylene glycol as the polyols instead of diethylene glycol. Issued as N.R.C. No. 5373. Presented at 32nd annual fall meeting, American Oil Chemists' Society, October 20–22, 1958, Chicago, Ill. National Research Council of Canada Postdoctorate Fellow, 1957     

Indirect Determination of Water in Nitroglycerin-Nitrocellulose Pastes by gas-liquid chromatography

A gas-liquid chromatographic procedure was developed in connection with the determination of water in nitroglycerin-nitrocellulose pastes. The method is based on the reaction of water with 2,2-dimethoxypropane and its conversion to acetone which is subsequently determined. The technique is simple, rapid, and shows good accuracy and precision. A simplified method, which is less accurate but does not involve chromatography, is also proposed.     

Application of gas-liquid partition chromatography to the quantitative estimation of monoglycerides

Summary A procedure has been developed for the quantitative estimation of monoglycerides in terms of their constituent fatty acids. The monoglyceride mixture is mesylated with mesyl chloride in the presence of pyridine, and the resulting dimesyl derivatives are converted to allyl esters of the constituent fatty acids by treatment with sodium iodide in anhydrous acetone at 100°C. The allyl esters are then analyzed quantitatively by gas-liquid partition chromatography at 240°C. on a column of Apiezon M—Celite. Both α- and β-monoglycerides are quantitatively converted to allyl esters by this procedure. β-Monoglycerides in a mixture of α- and β-isomers may be determined separately after removal of the α-isomers by oxidation with periodic acid. The analytical procedure is also applicable to monoglycerides in the presence of free fatty acids, diglycerides, and triglycerides. Issued as N.R.C. No. 5438. Presented at the 32nd fall meeting, American Oil Chemists' Society, Chicago, Ill., October 20–22, 1958. National Research Council Postdoctorate Fellow, 1956–1958.     

Gas-liquid chromatography of fatty derivatives. II. Analysis of fatty alcohol mixtures by gas-liquid chromatography

Conclusions Gas-liquid chromatography has been shown to be applicable to the analysis of fatty alcohols. Through the use of polyester columns these alcohols have been separated according to chain length and degree of unsaturation. A study has been made of the relationship between peak areas of the chromatograms and the actual weight percentages of the four C₁₈ alcohols found in the fatty alcohols derived from linseed oil. Fatty alcohols, prepared from soybean, linseed, and sperm oil have been prepared and analyzed by the proposed procedure. Craig and Murty (1) have recently reported that polyesters based on succinic acid are preferable for the liquid phase of the chromatographic column to those made from adipic in that they afford a better separation of methyl stearate from methyl oleate. Conversely adipic columns gave a more effective separation of the esters of linolenic and arachidic acids. The application of these polyesters to the analysis of fatty alcohol acetates is expected to improve their separation in a similar fashion, but further work is indicated in the search for a liquid phase that will permit both separations in the minimum time. ADM Technical Talk No. 166.