Rapid determination of double-bond positions in monoenoic fatty acids by periodate-permanganate oxidation

Tetramethylammonium hydroxide has been used in the extraction and pyrolysis methylation of the carboxylic acids produced by periodate-permanganate oxidation of monounsaturated fatty acid methyl esters. This modification of the von Rudloff procedure allows rapid determination of double-bond positions and analysis of mixtures of positional isomers of monoenoic fatty acids.     

The mass spectrometry of iso and anteiso monoenoic fatty acids

The normal, iso, and anteiso Δ⁸- and Δ⁹-17:1 fatty acid methyl esters were synthesized and their electron impact-induced fragmentation was studied by mass spectrometry. The mass spectra of the preterminal branched monoenoic fatty acid methyl esters present characteristic fragment ions, now understood to be indicative of the position of the methyl group. These fragment ions are in the iso compound m/e 227 [M-55]⁺, m/e 195 [M-87]⁺, and m/e 177 [M-105]⁺, while in the anteiso compound these fragments are shifted by 14 mass units to m/e 213, m/e 181, and m/e 163. The 15-D-iso Δ⁸- and Δ⁹-17:1 methyl esters were synthesized because the characteristic fragment ions in the methyl branched compounds indicated a key role of the tertiary hydrogen atom in the rearrangement process. A fragmentation mechanism consisting of a double bond migration triggered by the tertiary hydrogen and an allylic cleavage assuming a displacement mechanism is proposed.     

Characterization of branched-chain fatty acids from fallow deer perinephric triacylglycerols by gas chromatography-mass spectrometry

Branched-chain fatty acids of perinephric triacylglycerols of semi-feral fallow deer (Dama dama dama) were analyzed by high resolution gas chromatography-mass spectrometry. Of the total fatty acids, 15.50% were Branched-chain components including 8.96% iso acids, mostly 14-methylpentacanoic acid, 2.85% anteiso acids and 1.73% of other monomethyl-substituted acids; dimethyl-branched acids with an iso structure (1.05%) and with an anteiso structure (0.18%) were also present. Whereas the predominant iso acids and methyl-substituted iso acids had chain lengths of 13 and 15 carbon atoms, the anteiso acids and methyl-substituted anteiso acids had chain lengths of 14 and 16 carbon atoms. Methyl substitution occurred on the even numbered carbon atoms relative to the carboxyl group. The general composition is also given of the fatty acids comprising the triacylglycerols of subcutaneous (rump area) and perinephric adipose tissue.     

Lipoxygenase inhibition by naturally occurring monoenoic fatty acids

Lipoxygenase activity was not detected in preparations from several varieties of rapessed. Erucic acid, one of the main components of rapessed oil, competitively inhibited both soybean and peanut lipoxygenases. Various other long-chain monoenoic fatty acids were assayed for their effects on lipoxygenase activity with linoleic acid as substrate. Fatty acid chain length, from C₁₆, to C₂₄, was not a significant factor, but position of the point of unsaturation did affect enzyme activity. The position of the double bond from the carboxyl group seemed to be more significant than the distance between the point of unsaturation and the methyl terminal group in terms of inhibition.     

Identification of conjugated fatty acids by gas chromatography-mass spectrometry of 4-methyl-1,2,4-triazoline-3,5-dione adducts

4-Methyl-1,2,4-triazoline-3,5-dione was reacted with conjugated fatty acid methyl esters to form Diels-Alder cycloaddition products. The electron impact mass spectra of conjugated octadecadienoates and 9,11,13-octadecatrienoate were simple and informative and allowed the positions of the double bonds to be determined. The dienes gave single adducts whereas the triene formed four products that corresponded to two stereoisomers of the adducts of the 9,11-diene system and two of the 11,13-diene system. The method can be used to complement other methods for identifying conjugated fatty acids.     

Identification of sterols and bile acids by computerized gas chromatography-mass spectrometry

In mass spectrometry, sterols and bile acids form fragment ions characteristic of certain steroid structures. After separation of derivatized sterols or bile acids by the gas chromatograph and fragmentation in the mass spectrometer, data collected by the computer can be collated to provide a reconstructed gas chromatogram and a series of fragment ion current chromatograms in which the relative abundances of characteristic fragment ions are plotted vs time or scan number. Intensities of these fragment ions will be greatest and hence coincide with peak elution of unidentified sterols or bile acids. The use of known amounts of labeled appropriate sterols or bile acids permits quantitation of the identified sterol or bile acid.     

Gas chromatography-mass spectrometry methods for structural analysis of fatty acids

Procedures for structural analysis of fatty acids are reviewed. The emphasis is on methods that involve gas chromatography-mass spectrometry and, in particular, the use of picolinyl ester and dimethyloxazoline derivatives. These should be considered as complementing each other, not simply as alternatives. However, additional derivatization procedures can be of value, including hydrogenation and deuteration, and preparation of dimethyl disulfide and 4-methyl-1,2,4-triazoline-3,5-dione adducts. Sometimes complex mixtures must be separated into simpler fractions prior to analysis by gas chromatography-mass spectrometry. Silver ion and reversed-phase high-performance liquid chromatography are then of special value. In particular, a novel application of the latter technique, involving a base-deactivated stationary phase and acetonitrile as mobile phase, is described that is suited to the separation of fatty acids in the form of picolinyl ester and dimethyloxazoline derivatives, as well as methyl esters.     

Gas chromatography-mass spectrometry of methyl esters of unsaturated oxygenated fatty acids

Silylation of hydroxyl groups in methyl esters of unsaturated hydroxy acids provides compounds that give mass spectra which can be readily interpreted, whereas spectra of underivatized esters are extremely difficult to evaluate. The relationship of the double bond(s) to the trimethylsiloxy (TMS) group results in specific mass spectral patterns. In esters that have the TMS group separated from the double bond by one methylene group, the ions caused byα-cleavage at the TMS group on the side closest to the olefinic group are much more abundant than those produced fromα-cleavage on the other side of the TMS group. In esters that have the TMS group and the double bond separated by two methylene groups,α-cleavage ions are approximately equal. When the TMS group and the double bond are allylic, no fragmentation results between them. Cleavage does occur on either side of this system, and those ions resulting from cleavage alpha to the TMS group are in greatest abundance. Silylation of esters that have a conjugated diene or ene-yne system adjacent to a hydroxyl group also gives derivatives amenable to gas chromatographymass spectrometry. In these esters, large peaks are observed that arise fromα-cleavage at the TMS group and at the other end of the olefinic system. No fragmentation between the TMS group and the sites of unsaturation occurs. Unsaturated epoxy methyl esters produce spectra difficult to interpret. When the epoxide is converted to methoxy-hydroxy derivatives by BF₃-methanol, the spectrum locates the position of the epoxide group. Silylation of the hydroxyl group produces a compound that gives a less complicated spectrum which also locates the original epoxy group. Mass spectrometry of a series of unsaturated keto-esters, without derivatization, provides spectra that are easily interpretable. Presented at the AOCS Meeting, Los Angeles, April 1972. N. Market. Nutr. Res. Div., ARS, USDA.     

Capillary gas chromatography-mass spectrometry of resin acids in tall oil rosin

The resin acid composition of Finnish tall oil rosin was investigated by gas chromatography and mass spectrometry employing open tubular capillary columns. On a column coated with 1,4-butanediol succinate, 16 resin acids found in tall oil rosin samples were well resolved, and mass spectra could be recorded. All resin acids were confirmed to be of the pimaric and abietic types by gas chromatographymass spectrometry. Eight of the acids were not detected in the corresponding crude tall oils and evidently had been formed during the technical distillation process. The presence of 8,15-pimaradien-18-oic and 8,15-isopimaradien-18-oic acids in the rosin, but not in the crude tall oil, indicates that the pimaric type acids also undergo extensive isomerization during tall oil distillation. Additionally, three dihydroabietic acids and two acids with identical mass spectra, tentatively stereoisomers of 7,9(11)-abietadien-18-oic acid, were formed during the distillation process.     

Characterization of fatty acid isomers in dehydrated castor oil by gas chromatography and gas chromatography-mass spectrometry techniques

Fatty acid isomers present in dehydrated castor oil were analyzed by gas chromatography and gas chromatography-mass spectrometry (GC-MS) of their dimethyl oxazoline derivatives. Conjugated linoleic acid 9,11 and 10,12 isomers were identified by GC based on equivalent chainlengths. Segmental peak analysis of GC-MS total ion chromatogram mass fragmentation pattern revealed the presence of 7,9 and 8,10 conjugated linoleic acids along with 9,11 and 10,12 conjugated linoleic acids. Interestingly, a reverse elution of trans,trans-conjugated linoleic acids was observed, viz. 10,12 was followed by 9,11, which was in turn followed by the 8,10 and 7,9 isomers. The observed reverse order of elution was in contrast to the conventional elution pattern of both nonconjugated and conjugated cis,cis-, cis,trans- and trans,cis-isomers.     

A comparison of pyrrolidide and picolinyl ester derivatives for the identification of fatty acids in natural samples by gas chromatography-mass spectrometry

The pyrrolidide and picolinyl ester derivatives of the fatty acids in two natural lipid samples rich in unsaturated fatty acids, pig testis lipids and cod liver oil were satisfactorily resolved on capillary columns of fused silica coated with stationary phases of varying polarity. The picolinyl esters, in particular, when subjected to gas chromatography-mass spectrometry on a column containing a cross-linked methyl silicone, gave distinctive mass spectra, which could be interpreted in terms of both the numbers and positions of the double bonds.     

气质联用技术分析大兴安岭野生玫瑰花的脂肪酸组成

目的采用气质联用技术分析生长于黑龙江北部地区大兴安岭野生玫瑰花脂肪酸的组成。方法将同一天采摘并储存于相同条件下的野生玫瑰花,采用索氏提取法,以石油醚为溶剂对野生玫瑰花的不同部位萃取得到玫瑰花脂肪酸,经三氟化硼-甲醇酯化后,用气质联用技术进行定性和定量分析。结果野生玫瑰花不同部位(花瓣、花蕊、花托及花萼)的脂肪酸组成不同,花瓣中共检测出14种脂肪酸,其中不饱和脂肪酸相对含量为63.78%;花蕊中共检测出15种脂肪酸,其中不饱和脂肪酸的相对含量为59.1%;花托中共检测出13种脂肪酸,其中不饱和脂肪酸的相对含量为47.02%;花萼中共检测出20种脂肪酸,其中不饱和脂肪酸的相对含量为40.3%。结论野生玫瑰花不同部位(花瓣、花蕊、花托及花萼)的脂肪酸组成不同,花瓣部位富含不饱和脂肪酸,对提升玫瑰花精油的质量,充分利用野生玫瑰花资源提供了参考。     

Analysis of α-branched fatty acids by gas chromatography and mass spectrometry

Gas liquid chromatography and mass spectrometry were utilized in combination to identify isomeric α-branched chain fatty acid methyl esters. In a given isomeric series equivalent chain length, values decreased with increase in the number and size of α-alkyl substituents. Mass spectra of the α-monoalkyl derivatives are characterized by prominent McLafferty rearrangement ion peaks, whereas those of the α,α-dialkyl isomers contain the former ions plus an α-cleavage ion. Presented at the AOCS Meeting, Chicago, September 1973.     

Mass spectral studies of deuterium-labelled picolinyl fatty esters in the determination of double-bond positions

Deuteration (with Wilkinson’s catalyst) of methyl 12:1(3c), 14:1(5c), 18:1(9c), 18:2(9c,12c), 18:3(9c,12c,15c), 20:4(5c,11c,14c,17c), 20:5(5c,8c,11c,14c,17c) and 22:6(4c,7c,10c,13c,16c,19c) fatty acids gave the corresponding deuterium-labelled saturated fatty esters. The mass spectral analysis of their picolinyl esters gave clear diagnostic ion fragments, which permitted the facile and accurate determination of the positions of the double bonds (up to six) in the alkyl chain of the fatty ester.     

绿奇楠沉香成分GC/MS分析研究

采用乙醇浸泡提取绿奇楠沉香成分,并采用气相色谱质谱对绿奇楠化学成分进行分离鉴定,共鉴定出52种化合物,占成分总质量分数的85.052％,其中色酮类成分24种,主要成分为2-(2-苯乙基)色酮(质量分数为27.521％)、2-[2-(4-甲氧基)苯乙基]色酮(质量分数为24.224％)和2-[2-(3-羟基-4-甲氧基)...     

利用气相色谱-质谱联用技术测定微藻油脂的组成

采用超临界CO2萃取技术从微藻粉中提取油脂,微藻油脂经预处理后,采用气相色谱-质谱联用技术分析微藻油脂的组成成分.测定结果显示微藻油脂中主要有20种组分,主要是C12到C24的化合物,其中酯类化合物较多,以邻苯二甲酸二异辛酯居多,质量分数占70％以上,其次分别为反式角鲨烯、软脂酸等.     

Fatty acids of unusual double-bond positions and chain lengths found in rat skin surface lipids

The fatty acids of rat skin surface lipids comprise four main skeletal types of chains which occur both as saturates and monoenes and range from C₁₂ to C₃₈: straight even, straight odd, iso and anteiso (the latter two identified by GC retention data only). Two unidentified series of branched monoenes also occur in trace amounts. Reductive ozonolysis of monoenes reveals two characteristic double-bond position patterns, one for the straight even chain series and the other for the straight odd chain series. The straight even chain pattern comprises four series, of which ω7 ≫ω9>ω5>ω11; the straight odd chain series in contrast shows a large number of ω series with irregular distribution. The biosynthesis of the even chain fatty acid monoenes can be thought of as occurring in two stages: synthesis of 14∶Δ9, 16∶Δ9, 18∶Δ9 and 20∶Δ9, with 16∶Δ9 predominating; elongation of these chains mostly by 1, 2, or 3 C₂ units but up to the unusually long lengths by 11 C₂ units. For the formation of the former, two schemes by known pathways are proposed. Iso and anteiso chains which are nearly all saturated comprised 1/3 the total fatty acids. Special terms and abbreviations: Normal even=a straight chain with an even number of carbon atoms, normal odd=a straight chain with an odd number of carbon atoms, ω=terminal carbon atom, iso=a straight chain with a methyl group at the ω−1 position, anteiso=a straight chain with a methyl group at the w−2 position, Δn=a double bond between the n^th and the (n+1)^th carbon atom from the carbonyl group of the fatty acid or ester, ωn=a double bond between the ω∩n^th and the ω-(n−1)^th carbon atom where n is an integer, aldester=aldehyde methyl ester, Me=methyl, GLC=gas-liquid chromatography, TLC=thin-layer chromatography.     

气相色谱-质谱联用法测定儿童产品中残留的甲酰胺

采用甲醇作萃取溶剂,超声萃取样品中残留的甲酰胺,选用DB-VRX色谱柱进行目标物分离,质谱定量检测。建立了气相色谱-质谱（GC-MS）联用法快速测定儿童产品中残留的甲酰胺分析方法。考察了萃取方法、萃取溶剂、极性色谱柱对甲酰胺分离检测的影响。结果表明,在1~30 mg/kg内,线性关系良好（R2〉0.999 5）,重现性良好。在1~10 mg/kg甲酰胺添加水平内,平均回收率为86.7%~93.2%,相对标准偏差为4.4%~6.4%。甲酰胺的方法检出限为1 mg/kg。该方法快速简捷,易于操作,适用于进出口儿童产品的甲酰胺残留量的日常检测工作。     

Examination of acetolysis products of phosphatidylcholine by gas chromatography-mass spectrometry

A comparison of monoacetyldiglycerides obtained from authentic phosphatidylcholines by acetolysis with those obtained by phospholipase C-acetylation was made to examine the intermolecular acyl migration, the intramolecular acyl migration between C-1 and C-2, and the formation of 1,3-isomer in the acetolysis reaction. Egg yolk phosphatidylcholine also was used. It was revealed that is acetolysis, the intermolecular acyl migration and selective degradation of polyunsaturated fatty acids did not take place at all. The intramolecular acyl migration, including the formation of 1,3-isomer, occurred to a small extent. Appreciable difference was not found in comparison of molecular species compositions of monoacetyldiglycerides derived by both methods from egg yolk phosphatidylcholine, except small differences found in the contents of two kinds of molecular species.     

气相色谱-质谱联用法测定丁二烯中对叔丁基邻苯二酚含量

采用气相色谱一质谱联用(GC-MS)法测定丁二烯中阻聚剂对叔丁基邻苯二酚(TBC)含量,并与分光光度法和液相色谱法进行了比较.结果表明,用甲苯作为TBc的溶剂,其在被测组分的出峰区域不会形成干扰;采用选择离子模式检测可提高灵敏度.TBC质量分数为1×10-6～50×10-6时,外标法测定TBC含量的线性回归系数为0.999 5,加标回收率为98.60%～102.73%,相对偏差为2.42%～3.87%;GC-MS法与分光光度法、液相色谱法测得丁二烯中TBC含量相近,但GC-MS法更简便和快捷.