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     

Detection of trace fatty acids in fats and oils by urea fractionation and gas-liquid chromatography

The detection of trace fatty acids (<0.1%) in a fat or oil by gas-liquid chromatography is possible when the methyl esters are fractionated with urea to provide a number of less complex fractions. Identification and estimation of trace fatty acids is simplified by quantitative removal of other fatty acids having similar gas chromatographic retention times. A detailed knowledge of the order in which inclusion compounds are formed was obtained by fractionating a complex mixture of marine and vegetable fatty acids. In addition, lanolin was fractionated to determine the preferential order in which saturated, branched chain (iso-, anteiso-) and hydroxy acids form inclusion compounds. Using urea fractionation and gas chromatography, 52 trace fatty acids were tentatively identified in butter, 30 in lard, and 26 in walnut oil. Presented at the AOCS Meeting in New Orleans, 1964.     

Analysis of fats and oils by gas-liquid chromatography and by ultraviolet spectrophotometry

1. Known mixtures of pure fatty acid methyl esters and a number of fats and oils as their methyl esters have been analyzed by conventional GLC with thermal conductivity detectors.
2. Percentage of fatty acid distribution determined by GLC agreed well with known percentages in model mixtures and with analysis by the spectrophotometric method for fats and oils.
3. Determination of very small amounts of arachidonic and pentacnoic acids in lard by GLC was not successful.

     

Trans and polyunsaturated fatty acid content of some bakery fats

Twenty-seven commercial bakery products marketed in Belgium were analyzed by gas-liquid chromatography for their trans (TFA) and polyunsaturated fatty acid (PUFA) content. The mean PUFA level for the bakery fats in our study was 8.85% (S.D. = 9.90%) and the TFA content ranged from 0.0–18.81% (mean = 5.99%; S.D. = 5.02%). The unfavourable fatty acid profile of most of the analyzed bakery fats can be explained by the frequent use of animal fat and partially hydrogenated oils. The average daily intake of TFA from bakery products by the Belgian population was calculated at 0.43g/person/day. As it is expected that their consumption will increase in the future, lower TFA levels in bakery fats are necessary to avoid that these products become a more important dietary source of TFA.     

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).     

Near infrared spectral patterns of fatty acid analysis from fats and oils

A near infrared (NIR) spectral pattern of oil contains information about fatty acid composition, because NIR absorption bands around 1600–1800 nm and 2100–2200 nm are due to the straight carbon chain andcis double bonds, respectively. This study was undertaken to build a foundation for the rapid determination of the fatty acid composition in oil by an NIR method. First, NIR spectra of pure triglycerides were measured and characterized. Fatty acid compositions could be estimated roughly by comparing the spectra of fats and oils (butter fat, pig milk fat, soybean oil and palm oil) with those of pure triglycerides. Secondly, the NIR spectra of these fats and oils were reconstructed by summation of the triglyceride spectra, which are multiplied by factors corresponding to the fatty acid composition of the sample determined by gas chromatography. The calculated spectra agree with the originals, especially for that of soybean oil. However, in order to reconstruct spectra precisely, it may be necessary to reevaluate the loading weight of each triglyceride, which was equal in this study. Part of this study was presented at the 3rd International Conference on Near Infrared Spectroscopy on June 28, 1990, Brussels, Belgium.     

Component fatty acids and composition of some oils and fats

Nineteen different samples of oils and fats have been examined for their component acids and composition by gas-liquid chromatography. Under programmed-temperature operations, the temperatures at which different components start to elute bear a straight-line relationship with their respective carbon numbers. Chromatograms, under programmed-temperature conditions, of methyl esters from such oils as coconut, groundnut, mustard, etc., are used for identifying the components of an unknown oil by comparing its chromatogram taken under nearly identical conditions. For confirmatory identifications, such plots as logarithm of retention times versus carbon numbers for saturated acids (14:0 to 24:0), monoenoic acids (14:1 to 24:1), and dienoic acids (18:2 to 24:2), under isothermal conditions, have also been used. Some new fatty acids, noted for the first time in traditional oils, are 15:0 in cottonseed oil, 20:1 in sesame oil, 22:0 in soybean oil, and 24:2 in mustard oil. Odd-carbon chain acids from 11∶0 to 23:0 have been observed in such vegetable oils as peanut germ, rice bran, andMesua ferrea. Fatty acid composition by GLC for new samples like peanut lecithin, peanut germ oil,Myristica attenuata, Myristica kanarica, Myristica magnifica, Mesua ferrea, Vateria indica, Schleichera trijuga, and shark-liver stearine are presented. Industrial utilization of these new oils and fats is discussed.     

Gas liquid chromatography analysis of the fatty acid composition of fats and oils: A total system for high accuracy

The generally accepted approach to the analysis of fatty acid methyl esters (FAME) by gas liquid chromatography (GLC) is to analyze a standard mixture of known composition and to determine empirical correction factors for individual FAME. These correction factors, which are a composite of the theoretical flame ionization detector (FID) relative response factors and an empirical factor to correct for any system errors that may be present, then are used to correct the raw peak areas of the individual FAME of the sample undergoing analysis. It is proposed that this approach is fundamentally unsound as a means of generating consistently accurate results. Rather, it has been proven that theoretically calculated FID relative response factors are valid, both for the saturated and unsaturated FAME commonly encountered in edible oils, and that these should be used as the only response factors for the correction of raw peak areas. Thus, the proper approach to the generation of highly accurate results is to optimize both equipment and operator technique so that a correct answer is obtained for a primary standard when these theoretical factors are used, rather than to introduce an empirical correction factor other than the theoretical response factor to take account of faulty practice. Eight facets of equipment operation or operator technique have been identified which must be addressed to optimize accuracy. Presented at the 77th Annual AOCS Meeting in May 1986 in Honolulu, Hawaii.     

Antioxidants for food fats and oils

Types of antioxidants currently available for food fats and oils are listed, and theoretical and practical aspects of selecting the proper ones for various food uses are reviewed. Consideration is given to relative potencies, modes of application, regulations governing use, and some of the more prominent problems encountered in their commercial applications. A brief look is taken into future needs and possible developments with fat and oil antioxidants. One of seven papers presented in the symposium “Fats and Oils in Food Industry,” AOCS Meeting, Atlantic City, October 1971.     

Determination of trace amounts of fatty acids in edible oils by capillary gas-liquid chromatography

The effect of using different gas-liquid chromatography (GLC) hardware to quantify low concentrations of fatty acids was studies. A fused-silica capillary column was operated in two different chromatographs (A and B) that were interfaced to three different chromatographic data systems to process the flame-ionization detector signals (systems A, B1, and B2). A test routine was developed that allowed the proper selection of peak processing parameters for the automatic recognition and integration of fatty acids occurring at trace levels. However, agreement of analytical results between the three analytical systems was not satisfactory; components at concentrations <0.10 g/100 g could not be quantified with high reliability, although the same capillary column and identical sample solutions were used (quasi-repeatability conditions). Even for major fatty acids, deviations up to 1.0 g/100 g were noted, which could only be attributed to the use of different GLC hardware. Attention should be paid to these technical restrictions when formulating product specifications based on fatty acid profile parameters.     

Determination of nitrogen content of fats and oils by the method of combustion/ion chromatography

A method of combustion/ion chromatography (C/IC), initially developed for the determination of sulfur, has been extended to determination of total nitrogen in fats and oils. It is shown that nitrogen gas dissolved in the sample interferes with the determination, and that it is necessary to degas the sample before analysis. Moreover, there is a procedural blank for the nitrogen in the cylinder oxygen employed. Despite these drawbacks, the method has advantages over conventional methods, in that (i) measurements can be carried out with standard laboratory equipment, and (ii) nitrogen and sulfur, and possibly halogens and selenium, can be determined simultaneously.     

Fatty acid distribution of fats,oils and soaps by high-performance liquid chromatography without derivatization

A high-performance liquid chromatography (HPLC) procedure without derivatization was developed for quantitating fatty acid components of various soap-related fats and oils, as well as for the direct quantitation of fatty acids from soap. The fatty acids are detected by refractive index after isocratic reverse-phase chromatography. The method has been developed with radial compression and stainless-steel column technology. The triglycerides are saponified and acid-hydrolyzed into fatty acids, and they are dissolved in a solvent and injected. The soaps are dissolved in methanol and injected into the HPLC, where they are acid-hydrolyzed directly on the column by an acid-modified mobile phase. The total run time after injection is approximately 20 min, with quantitation performed on an NEC Powermate^® computer driven by PE/Nelson Analytical Software. The typical carbon chains analyzed are from C6 to C20.     

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.     

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.     

Analysis ofcis- andtrans-fatty acid isomers in hydrogenated and refined vegetable oils by capillary gas-liquid chromatography

For quantitation ofcis- andtrans-fatty acid isomers, infrared (IR) spectroscopy, gas-liquid chromatography (GLC) on highly polar stationary phases or the combination (GLC-IR) may be used. IR offers the advantage of simplicity and speed, but the lower determination limit of 5% and the lack of detailed information limit its use. Detailed fatty acid information, required for, e.g., food-labeling purposes, can only be obtained with GLC methods. Most of the GLC methods are optimized for partially hydrogenated samples. AOCS Official Method Ce 1c-89 prescribes a single, highly polar stationary phase, SP2340, but underestimates the amount oftrans isomers due to 18∶1 positional isomer overlap. The combined GLC-IR method may circumvent this problem but at the cost of time, effort, and precision.Trans isomers in refined (deodorized or stripped) oils are different in type and levels from isomers in partially hydrogenated oils; theirtrans isomers are mono-trans trienoic and dienoic isomers, occurring at levels up to about 1–3%. GLC conditions for hydrogenated samples are often not suitable for refined oils because of overlap problems, but this time in the 18∶3 region. Through careful selection of stationary phase and temperature program optimization (Drylab^®GC), we have developed a single method that is suitable for hydrogenated, as well as refined, processed oils. The accuracy was checked withcis andtrans fatty acid fractions isolated by silverion exchange high-performance liquid chromatography. Thetrans values obtained with the optimized method are in good agreement with the results obtained for the isolated fractions. We propose that recommended methods describe GLC conditions in terms of separation criteria rather than recommending only a fixed combination of stationary phase and temperature program.     

The 9-hexadecenoic and 11-octadecenoic acid content of natural fats and oils

The monoenoic methyl esters from numerous fats and oils which contained appreciablecis-9-hexadecenoic acid (cis-9-16∶1) were isolated by liquid-solid chromatography on silver nitrate-silica gel. Analysis of the monoenes by packed and capillary column gas-liquid chromatography showed that significant amounts ofcis-11-octadecenoic acid (cis-11-18∶1) were present in all samples. The amount ofcis-11-18∶1 found in the monoenoic methyl esters increased proportionally to logarithmic increases in thecis-9-16∶1 level. Most analyses reported in the literature also show this proportionality. This mathematical relationship suggests that chain elongation ofcis-9-16∶1 tocis-11-18∶1 is a biosynthetic pathway operative in a wide variety of species.     

Quantitative determination of traces of free gossypol in fats,oils, and fatty acids by paper chromatography

Summary A quantitative method for the determination of traces of free gossypol in oils and fatty acids was developed. The method is based on the concentration of gossypol by extraction and quantitative paper chromatography of the extract. The method is specific for free gossypol and is not subject to interferences. The new method is both accurate and reproducible. The lower limit of detection is 10 p.p.m. The method is intended primarily for p.p.m. levels but is suitable for all concentrations. With slight modifications the method is applicable to meals. Presented at the fall meeting of the American Oil Chemists’ Society, Cincinnati, O., September 30 to October 2, 1957.