Hydrazine reduction in the gas liquid chromatographic analysis of the methyl esters of cyclopropenoic fatty acids

Hydrazine was used to hydrogenate the double bond of cyclopropenoic fatty acids (CPEFA) without cleaving the cyclic system. Using gas liquid chromatography (GLC), quantitation studies showed that it was possible to accurately determine CPEFA at concentrations as low as 0.1%. Studies with kapok seed oil methyl esters illustrated the potential application of such a technique to selectively hydrogenate the CPEFA to cyclopropanoic fatty acids (CPAFA), rendering them stable on the column, with a minimum effect on the degree of unsaturation of the remaining double bonds. Hydrazine reduction was found to be a simple and accurate method of measuring CPEFA in seed oils. Decomposition of pure methyl sterculate (methyl 9,10-methylene-9-octadecenoate) on GLC columns of various polarities also was examined.     

Comprehensive two dimensional gas chromatographic separation of fatty acids methyl esters with online reduction

The accurate analysis of complex fats and oils often requires combining data from multiple GC separations, fractionation by LC prior to GC analysis, and identifying fatty acids or confirming their identities by mass spectrometry and synthetic reference materials. Comprehensive two dimensional gas chromatography markedly increases the number of resolved fatty acid methyl esters (FAME) in a single separation experiment by combining the separations of two capillary columns. The addition of a capillary reducer in front of the second capillary column provides unique separation patterns and structural information for fatty acids based on simple elution rules.     

Application of specific response factors in the gas chromatographic analysis of methyl esters of fatty acids with flame ionization detectors

The relative responses for flame ionization detectors in the analysis of the longer chain fatty acid methyl esters are shown to correlate with the theoretical responses based on weight percent content of “active” carbon. While particularly affecting estimation of the shorter chain length saturated fatty acids, these corrections have a less marked effect on the estimation of unsaturated fatty acids.     

Rapid gas-liquid chromatographic procedure for the analysis of methyl esters of long chain fatty acids

A gas-liquid chromatographic procedure permitting rapid analysis of the major fatty acids commonly found in vegetable oils was evaluated with standards of known composition and found to be both accurate and precise. A standard containing 20% by weight of each of the methyl esters of palmitic, stearic, oleic, linoleic, and linolenic acid was analyzed in 2.7 min with errors of 1.6, 0.7, 3.3, 0.8, and 3.1%, respectively. Six procedures, requiring from 2.7 to 25 min for the eluation of the effects of the operational parameters, carrier gas flow rate and column temperature, on the precision and accuracy of gasliquid chromatographic analysis of fatty acid methyl esters. The most rapid procedure, obtained with a column temperature of 235C and a helium flow rate of 110 ml/min was found to be comparable in accuracy and precision to the other procedures and gave quantitative results with National Heart Institute type fatty acid standards KA, KB, and KD, that agreed with stated composition with a relative error of less than 2% for major components (10% or more of total mixture) and less than 6% for minor components (less than 10% of total mixture). Approved as Journal Series Paper No. 535, Georgia Experiment Station. This research was supported in part by Corn Industries Research Foundation and by Corn Products Company.     

Homogeneously catalyzed hydrogenation and gas-liquid chromatographic analysis of the methyl esters of cyclopropene fatty acids

Various concentrations of cyclopropene fatty acids have been determined down to 0.2% by the use of gas liquid chromatographic (GLC) analysis of the methyl esters of fatty acids that have been quantitatively hydrogenated using a homogeneous transition metal complex catalyst. The effectiveness of the use of bromotris(triphenylphosphine)-rhodium(I), Br(P(C₆H₅)₃)₃Rh, as a homogeneous hydrogenation catalyst to convert the cyclopropene ring to a cyclopropane ring has been evaluated and compared with the analogous chloro- and iodo-complexes. The hydrogenation/GLC method of analysis has been compared with the method of titration with hydrogen bromide in benzene and with the method involving the use of high resolution nuclear magnetic resonance (NMR).     

Autoxidation of methyl esters of cyclopentenyl fatty acids

The early stages of the autoxidation of methyl hydnocarpate, chaulmoograte and gorlate in air have been examined at 40, 60 and 80 C, and the initial products have been compared by several methods with those derived from methyl oleate and linoleate autoxidized at 60 C. To supplement information about oxygen absorption and peroxide development in relation to time, other information about the early products, and some information about the reduced products, have been obtained by ultraviolet (UV) and infrared (IR) spectrophotometry, and by thin layer chromatography (TLC). The kinetic and other data presented in this study strongly support the conclusion that the methyl esters of cyclopentenyl fatty acids yield initial autoxidation products that, although they are primarily peroxides, differ in some ways (as expected) in the kinetics of their formation and their chemical nature, compared to those of oleate and linoleate. Nevertheless, all the data obtained strongly support the surmise that the peroxides are formed autocatalytically by a chain mechanism, and that secondary products not derived from peroxide decomposition, are formed pari passu in lesser, but increasing amounts with increasing temperature, probably from free radical intermediates. The autoxidation of esters of cyclopentenyl fatty acids has potential importance in several ways, 3 of which are mentioned briefly.     

Determination of physicochemical properties of some fatty acid methyl esters by gas liquid chromatography

Physicochemical data such as vapor pressures (p⁰), heats of vaporization (ΔH_v), activity coefficents at infinite dilution (γ^∞) and excess partial molar entropy (ΔS _e ⁰ ) are considered important for conducting unit processes and designing reactor equipment. Scanty information regarding such data is available in the literature for the higher fatty acid methyl esters. The objective of this research was to determine the physicochemical properties of higher fatty acid methyl esters (C₁₁–C₂₃) by a gas-liquid chromatographic technique with SE-30 and diethylene glycol adipate as stationary phases. Correlations between carbon numbers and various thermodynamic properties have indicated definite trends, which could be useful in predicting the properties of unknown fatty acid methyl esters. The data generated may be useful to chemical engineers in the construction of storage tanks, solvent extractors and distillation columns. IICT communication no. 2993.     

The amplified distillation of methyl esters of fatty acids

Summary Amplified distillation is a useful technique for the quantitative analysis of mixtures of fatty acid esters, especially for the detection and estimation of minor components and for the analysis of small samples. The amplified distillation of free fatty acids is largely limited to qualitative work on account of the formation of azeotropes with mineral oils. Presented before the 1945 Fall Meeting of the American Oil Chemists' Society, Chicago, Ill.     

Precision and accuracy in gas liquid chromatography of C14-C18 fatty methyl esters

Repetitive analyses of four primary standards for fatty methyl esters by gas liquid chromatography (GLC) with polyester columns and thermal conductivity detection established standard deviations ranging from ±0.3–0.5% corresponding to coefficients of variation of 1.0–2.0%. These data, representing a relative error of measurement of 1.5–3.0% at a 99% confidence level, suggest a precision approaching that of conventional spectrophotometric measurements. Proportionality factors, calculated from known mass or molar concentration divided by area % from GLC analysis, were found to be reproducible correction factors which may be generally applicable to GLC analysis of fatty methyl esters with polyester columns and thermal conductivity detectors. Mass response to a thermal conductivity detector was found to decrease with either increasing molecular weight for saturated C₁₄–C₁₈ fatty methyl esters or with unsaturation among the C₁₈ unsaturated esters, while molar response increases with molecular weight and decreases with degree of unsaturation. The use of uncorrected area % data can introduce significant absolute mass errors ranging from about +11% for myristic acid to −17% for linolenic acid. Presented at the AOCS Meeting, New Orleans, La., April 1964. So. Utiliz. Res. and Dev. Div., ARS, USDA.     

Determination of tocopherol in autoxidizing methyl esters of fatty acids

Summary Autoxidizing methyl esters of fatty acids interfered with the determination of α-tocopherol by ultraviolet spectrophotometry or by the bipyridine colorimetric method. Interference with the colorimetric method was removed by sulfuric acid treatment, but spectrophotometry was applicable only when the tocopherol was completely separated from oxidized fat. This separation could not be obtained by sulfuric acid treatment but was accomplished by room temperature saponification in an alcohol-petroleum ether system protected by pyrogallol. The sensitivity of the spectrophotometric method was increased by oxidizing tocopherol quantitatively to thep-quinone with 2N nitric acid. N. R. C. No. 4053. Presented in part at meeting of American Oil Chemists’ Society, Minneapolis, Minn., Oct. 11–13, 1954.     

Comparison of FTIR and capillary gas chromatographic methods for quantitation oftrans unsaturation in fatty acid methyl esters

A computer-assisted method has been developed for estimation of isolatedtrans unsaturation using the peak area of thetrans absorbance band at 966 cm-1from FTIR spectra of fatty acid methyl esters. Peak areas were used to determine thetrans content of weighed standards containing from 0 to 100% methyl elaidate and of hydrogenated soybean oil samples containing up to 36%trans unsaturation. These data for percenttrans by FTIR were compared to corresponding data obtained by capillary gas chromatography and the AOCS Official Method 14-61. Determination of isolatedtrans composition in oils using peak areas gave values with the smallest standard deviation for weighed standards and values within 4% of those obtained by capillary gas chromatography and the AOCS Official Method for hydrogenated samples. Presented at the AOCS meeting in Phoenix, AZ in May 1988. To whom correspondence should be addressed.     

Silver nitrate-high performance liquid chromatography of fatty methyl esters

Long chain fatty methyl esters have been separated by high performance liquid chromatography on the basis of number, position, and geometric configuration of double bonds with a silver nitrate-silicic acid column and benzene solvent. Saturated esters are eluted first, followed by methyl elaidate and then methyl oleate. Geometric isomers of methyl 9,12-octadecadienoate and of methyl 9,15-octadecadienoate are also well separated. Methyl linolenate is retained strongly on the column and its elution has not been observed, but thetrans, trans, trans andtrans, cis, trans isomers are separated.     

Computer processing of gas chromatographic data: Quantitative analysis of fatty acid methyl esters using an off line magnetic tape system

This paper describes the off line processing of chromatographic data from fatty acid methyl ester mixtures by a large digital computer. The output of the gas chromatograph is recorded and stored on magnetic tape; the tape can then be processed at any convenient time. The system takes the analog signal from the electrometer and converts it to digital form, adds a time base and records the data using an incremental magnetic tape recorder. The data sampling rate can be varied from 0.05 to 5 times per second. The total number of samples per tape is limited only by the length of the tape. A 1200 ft reel can store up to 30 hr of gas chromatographic runs. The tape is processed by a CDC-6600 computer. The computer locates all peaks, determines the retention time and calculates the mass percentage of each peak. Along with the numerical output, a cathode ray tube plot of the data is also generated by the computer. The program has provisions for baseline corrections and peak overlap. The program also incorporates corrections for detector nonlinearity and variation in detector response to different molecular species. The accuracy of the system is within 5% based on analysis of fatty acid methyl ester samples of known composition. Computation time for a 1200 ft reel of tape is approximately 20 min. One of seven papers to be published from the Symposium ‘Computer Systems and Applications in the Oil and Fat Industry,’ presented at the ISF-AOCS Congress, Chicago, September 1970.     

Copolymerization of methyl esters of unsaturated C18 fatty acids

In order to assay the possibilities of making high polymers from linseed oil, the copolymerizations of styrene with the methyl esters of oleic, linoleic, linolenic, and conjugated linolenic acids were studied at 60–130C and copolymerizations of the last three esters with acrylonitrile were studied at 60C. Appropriate free radical initiators were employed in all cases. The esters without conjugated unsaturation show little tendency to enter a copolymer with styrene, but copolymers containing up to 40% by weight of conjugated linoleate can be obtained. Linoleic, linolenic, and conjugated linoleic esters copolymerize readily with acrylonitrile. Products containing up to 45 mole %, 80 wt %, of the conjugated ester can be made. However, methyl eleostearate, with three conjugated double bonds, inhibits the polymerization of both styrene and acrylonitrile. Quantitative comparisons of the behaviors of the esters are made through the copolymerization equation. The probable performance of these and other vinyl monomers in copolymerization with linseed oil is discussed. Presented at the Symposium on Recent Advances in Drying Oil Chemistry, Division of Organic Coatings and Plastics Chemistry, Am. Chem. Soc. meeting in Washington, 1962.     

High performance liquid chromatographic separation of sucrose fatty acid esters

The synthesis of sucrose fatty acid esters always results in complex mixtures. Two procedures for quantitative analysis of sucrose monoesters, respectively sucrose diesters, by means of high performance liquid chromatography on reversed-phase columns, are described. A mixture of methanol and water (85:15, v/v) was used for the separation of the monoesters, while methanol, ethyl acetate and water (65:25:10, v/v/v) was used for the separation of diesters. These methods gave information about the amount of monoesters and diesters in the product; the ratio between sucrose monopalmitate and sucrose monostearate, and the number of the most important structure isomers. A complete separation of all the possible diester products seemed to be impossible, due to the presence of more complex structure isomers. The described procedures can give important support during preparative work on sucrose fatty acid esters and also in the evaluation of these products for application purposes.