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.     

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.     

13C nuclear magnetic resonance of mono-and dihydroxy saturated and unsaturated fatty methyl esters

¹³C nuclear magnetic resonance spectra were obtained for methyl esters oferythro- andthreo-9,10-dihydroxystearates, for 12-hydroxy-cis- andtrans-9-octadecenoates, and forthreo-12,13-dihydroxy-cis-andtrans-9-octadecenoates.Erythro andthreo compounds may be distinguished easily by the difference in the chemical shifts of the carbons alpha to the hydroxy-bearing carbons. Monohydroxy compounds are easily distinguished fromvicinal dihydroxy compounds by differences in chemical shifts of both the hydroxy-bearing carbons and of the carbons alpha to them. The presence of a hydroxy-bearing carbon beta to a double bond results in the two carbons of the double bond of a hydroxy-bearing carbon beta to a double bond results in the two carbons of the double bond having different chemical shifts, with the numerical values being different for thecis andtrans isomers. The chemical shift of a carbon alpha to both a doubly bonded carbon and a hydroxy-bearing carbon is influenced both by the geometry of the double bond and the number of hydroxy-bearing carbons. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

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.     

A simple method of preparation of methyl trans-10,cis-12- and cis-9,trans-11-octadecadienoates from methyl linoleate

Pure conjugated isomers of linoleic acid were prepared on a large scale by alkali-isomerization of purified methyl linoleate. The methyl esters of alkali-isomerized linoleic acid contained mainly the methyl cis-9,trans-11- and trans-10,cis-12-octadecadienoates (44 and 47%, respectively). These two isomers were then separated and purified by a series of low-temperature crystallizations from acetone. The isomeric purity obtained for the cis-9,trans-11-octadecadienoate isomer was >90% and that of the trans-10,cis-12-octadecadienoate isomer was 89 to 97%. The isolated yield of the two isomers corresponded to 18 and 25.7%, respectively, of the starting material. The structure of the two isomers was confirmed using partial hydrazine reduction, silver nitrate-thin-layer chromatography of the resulting monoenes and gas chromatography coupled with mass spectrometry of the 4,4-dimethyloxazoline derivatives. Fourier transform infrared spectroscopy of the monoenes gave the confirmation of the geometry of each double bond.     

New developments in silver resin chromatography ofcis andtrans fatty methyl esters

Chromatographic separations of geometric isomers of methyl octadecenoates and octadecadienoates on a silver-treated macroreticular resin are much improved with newer resins of greater surface area and ground to a smaller particle size.cis,cis-Dienes can be recovered in practical elution volumes. With methanol as solvent small molecules including even radioactive methanol are retarded on the column relative to methyl esters of saturated acids. Presented at the AOCS Meeting, Chicago, September 1976.     

Large-scale synthesis of methyl cis-9, trans-11-octadecadienoate from methyl ricinoleate

The conjugated linoleic acid methyl cis-9,trans-11-octadecadienoate has been prepared on a large scale from methyl ricinoleate. Methyl ricinoleate was purified from castor esters by a partition method. It was converted to the mesylate, which was reacted with a base (1,8-diazabicyclo[5,4,0]-undec-7-ene) to give a product that contained 66% of the desired ester. Two urea crystallizations produced a product containing 83% methyl cis-9,trans-11-octadecadienoate, the identity of which was confirmed by gas chromatography linked to mass spectrometry and by Fourier transform infrared spectroscopy. The remaining impurities were methyl cis-9,cis-11- and cis-9-,trans-12-octadecadienoate.     

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).     

An improved reversed-phase thin-layer chromatography method for separation of fatty acid methyl esters

Resolution of fatty acid methyl esters (FAME) by thin-layer chromatography often is complicated by co-migration of certain acyl-isomers in heterogeneous mixtures. However, a novel reversed-phase thin-layer chromatography method which employs 10% (wt/vol) silver nitrate in a mobile phase containing acetonitrile/1,4-dioxane/acetic acid (80:20:1, vol/vol/vol) allows one-dimensional resolution of a wide range of acyl-methyl esters. This innovation enables improved separation of saturated FAME ranging from C₁₂ to C₂₂, and geometric isomers of C₁₄ to C₂₂ unsaturated FAME by thin-layer chromatography.     

Improved separation of conjugated fatty acid methyl esters by silver ion-high-performance liquid chromatography

Operating from one to six silver ion-high-performance liquid chromatography (Ag⁺-HPLC) columns in series progressively improved the resolution of the methyl esters of conjugated linoleic acid (CLA) isomeric mixtures from natural and commercial products. In natural products, the 8 trans, 10 cis-octadecadienoic (18∶2) acid was resolved from the more abundant 7 trans, 9 cis-18∶2, and the 10 trans, 12 cis-18∶2 was separated from the major 9 cis, 11 trans-18∶2 peak. In addition, both 11 trans, 13 cis-18∶2 and 11 cis, 13 trans-18∶2 isomers were found in natural products and were separated; the presence of the latter, 11 cis, 13 trans-18∶2, was established in commercial CLA preparations. Three Ag⁺-HPLC columns in series appeared to be the best compromise to obtain satisfactory resolution of most CLA isomers found in natural products. A single Ag⁺-HPLC column in series with one of several normal-phase columns did not improve the resolution of CLA isomers as compared to that of the former alone. The 20∶2 conjugated fatty acid isomers 11 cis, 13 trans-20∶2 and 12 trans, 14 cis-20∶2, which were synthesized by alkali isomerization from 11 cis, 14 cis-20∶2, eluted in the same region of the Ag⁺-HPLC chromatogram just before the corresponding geometric CLA isomers. Therefore, CLA isomers will require isolation based on chain length prior to Ag⁺-HPLC separation. The positions of conjugated double bonds in 20∶2 and 18∶2 isomers were established by gas chromatography-electron ionization mass spectrometry as their 4,4-dimethyloxazoline derivatives. The double-bond geometry was determined by gas chromatography-direct deposition-Fourier transform infrared spectroscopy and by the Ag⁺-HPLC relative elution order.     

Gas chromatographic separation of cholesteryl esters of fatty acids of different degrees of unsaturation

Cholesteryl esters prepared from the fatty acid methyl esters of linseed oil, pig liver lipids, and Japanese anchovy oil have been separated on the basis of their chain lengths and number of double bonds by gas lipid chromatography on a cyanosiloxane SILAR 10C column. The equivalent chain lengths of cholesteryl esters having acyl groups with 14–22 carbons and 0–6 double bonds are presented. A significant influence of the column temperature on the equivalent chain lengths of the polyenoic fatty acid cholesteryl esters has been found. Separation of the cholestanyl and epicholestanyl esters of linseed oil fatty acids, respectively, under the same conditions is also described.     

Gas-liquid chromatographic separation of ethylene oxide adducts of fatty alcohols via their acetate esters

Gas-liquid chromatography (GLC) of ethylene oxide adducts of fatty alcohols is carried out after conversion of the alcohols to aetate esters. This conversion permits detection of higher mol wt compounds. Separate peaks for adducts with up to 13 units of ethylene oxide are obtained for a product derived from dodecyl alcohol. The procedure is used to follow the course of a molecular distillation of an adduct prepared from hexadecyl alcohol and an example is also shown for an adduct derived from a mixture of dodecyl and tetradecyl alcohols. Presented at the AOCS Meeting in Minneapolis, 1963.     

A chromatographic method for the analysis of propylene glycol fatty acid esters in shortenings containing mono- and diglycerides

A procedure is described for the separation, identification, and quantitative estimation of propylene glycol mono- and diesters of lauric, myristic, palmitic, stearic, and oleic acids in shortenings and lard containing mono- and diglycerides. Lipid classes are separated on a silicic acid column, and individual esters are estimated by gas chromatography. Analyses of several control mixtures and commercial samples are reported. Recoveries for individual components range from 92 to 105%, and total recoveries range from 96 to 100%.     

Chromatographic separation ofcis andtrans fatty esters by argentation with a macroreticular exchange resin

Methyl oleate and methyl elaidate, as well as other monoenecis andtrans isomers of fatty esters, can be separated quickly and conveniently by a preparative chromatographic procedure in which a silver-saturated ion-exchange resin is used. Separations are based on differences in stabilites of the silver-olefin complexes. Recoveries of better than 95% were made, and puretrans andcis monoene fractions were collected. This method can be used to separate saturates fromcis andtrans monoenes. Thecis,trans,cis,cis, andtrans,trans-9-12-octadecadienoates were separated. Whilecis,trans andtrans,trans dienes were cluted separately, thecis,cis diene isomer remained on the column. Presented at AOCS Meeting, in Minneapolis, 1963. A laboratory of the No. Utiliz. Res. and Dev. Div., ARS, USDA.     

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.     

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.     

Mass spectra of diterpene resin acid methyl esters

The mass spectra of 35 tricyclic, diterpene resin acid methyl esters were examined. It was found that unsaturation substantially influenced the initial fragmentation. The carbomethoxy group is readily eliminated, with the positive charge usually being retained in the cyclic fragment. No significant differences were noticed among stereoisomers. Presented in part at the Meeting of the American Chemical Society, Chicago, September 1970.     

Performance of sulfoxylated fatty acid methyl esters

Sulfoxidation of fatty acid methyl esters with SO₂, O₂, and ultraviolet light of appropriate wavelength has led to the synthesis of methyl esters sulfonates or sulfoxylates known as Φ-MES because of the possible random position of SO₃ group in the alkyl chain. This work describes experimental measurements of physical properties such as solubility and viscosity of sodium Φ-MES water solutions. Amphipathic properties such as surface tension, critical micelle concentration, wetting and foaming powers were measured as well and compared to linear alkylbenzene sodium sulfonate (LAS). Finally, stability to water hardness, dishwashing test, and detergency performance were evaluated. Expectedly, these products may be used as LAS partners either in heavy-duty powders or in hand dishwashing liquids. Experimental results on Φ-MES of varying carbon number indicate that C₁₆ is the optimal carbon chain length.     

Dilatometric investigations of fatty acid methyl esters

Summary The coefficients of expansion and melting dilations were measured for methyl palmitate, methyl stearate, methyl arachidate, methyl behenate, and methyl oleate. The dilatometric curve for the heating cycle of methyl palmitate and methyl stearate in the solid state was composed of a linear section to 49 degrees below the melting point, followed by a curvilinear section to the melting point. The heating and cooling cycle curves for methyl palmitate show the same volume change from −38°C. to 29°C., but the shape of the curves is different. The same relation holds for methyl stearate from −38°C. to 37.5°C. “After-contractions” were found in volume measurements within a few degrees of the melting point of both esters. Equilibrated points were found within 0.5 degrees of the final melting temperature of methyl stearate. A striking similarity exists between curves for variation of the dielectric constant with temperature for long chain linear molecules and the dilatometric data. Presented at the fall meeting, American Oil Chemists' Society, Mnneapolis, Minn., October 11, 1954. Issued as Paper No. 196 on the “Uses of Plant Products” and as N.R.C. No. 3671.