Analysis of volatile fatty acids in biological specimens by capillary gas chromatography

A method was developed to analyze and quantitate volatile fatty acids such as acetic, propionic, butyric, iso-butyric, valeric, and iso-valeric acid from samples of biological origin. A capillary column system including an automatic on-column injection device as well as a precolumn of larger internal diameter than the analytical column was elaborated for this purpose. In order to obtain well resolved and correctly quantifiable chromatographic peaks it turned out to be essential to work under acidic/aqueous conditions. To achieve a better sample transfer into the chromatographic system an organic solvent had to be used together with the aqueous milieu, thus improving wetting properties of the liquid sample plug introduced into the column. Cold on-column injection was applied in order to avoid discrimination of the various acids due to sample splitting and the automatic technique was chosen in view of the large number of samples from biological extractions which had to be analyzed.     

Simultaneous determination of C2-C22 non-esterified fatty acids and other metabolically relevant carboxylic acids in biological material by gas chromatography of their benzyl esters

A method for the simultaneous determination of non-esterified short-, medium- and long-chain fatty acids and other types of metabolically relevant carboxylic acids such as hydroxy, keto, aromatic and dicarboxylic acids in biological material by capillary gas chromatography of benzyl ester derivatives is described. Sample preparation avoiding incomplete isolation of carboxylic acids consisted of deproteinization and extraction with ethanol, fixation of carboxylic acids as carboxylates, removal of interfering compounds such as neutral lipids by hexane extraction and amino acids, acyl carnitines and other cations by cation-exchange chromatography, derivatization of keto groups of ketocarboxylic acids into O-methyl oximes and benzyl ester formation by reaction of the potassium carboxylates with benzyl bromide via crown ether catalysis. The sample preparation conditions were investigated, showing the usefulness of this method for quantitative determinations. Chromatograms obtained from human serum, human urine and rat heart ventricle and concentrations of carboxylic acids in these specimens are presented.     

气相色谱法测定生物柴油中脂肪酸甲酯含量

生物柴油是利用动植物油脂等可再生资源通过酯交换技术制造的可以替代石化柴油的新型清洁安全燃料[1-3]它的主要成分是脂肪酸甲酯。由于不同油脂原料所生产的生物柴油的脂肪酸甲脂组成不同因而测定时所需的气相色谱条件与方法也不尽相同[4-6]。本文采用HP-innowax毛细管色谱柱,     

Analysis of volatile fatty acids by gas chromatography separation of benzyl esters

Volatile fatty acids in aqueous media were esterfied in situ with phenyldiazomethane (PDM). Complete esterification was achieved in 3 h at 40°C under continuous stirring of an ether/water system. The process involved immediate transfer of benzyl esters into the organic phase. The separation of benzyl esters mixtures was carried out in glass capillary GC columns. The retention data and FID molar responses were determined for C1 to C6 acid benzyl esters, including 2-methylpropionic, 3-methylbutyric, 2-methylvaleric, and 2-ethylbutyric acid. An unusual relationship was observed between benzyl ester relative molar responses and carbon atom number.     

On-line hydrogenation of fatty acid methyl esters in capillary gas chromatography

An injection splitter in front of a glass capillary column was used for the hydrogenation of fatty acid methyl esters (FAME) mixtures. Hydrogenation followed by gas chromatographic analysis on capillary columns permitted detection and identification in complicated natural mixtures of branched fatty acids, showing minor structural differences, in quantities down to 10^?8g. The technique described, apart from its suitability for FAME analysis, shows promise for structure determination studies of other classes of compounds.     

Chromatographic efficiency of polar capillary columns applied for the analysis of fatty acid methyl esters by gas chromatography

The chromatographic efficiency that could be achieved in temperature‐programmed gas chromatography was compared for four capillary columns that are typically applied for analysis of fatty acid methyl esters (FAME). Three different carrier gases, hydrogen, helium and nitrogen, were applied. For each experiment, the carrier gas velocities and the temperature rates were varied with a full 9 × 3 design, with nine levels on the carrier gas velocity and temperature rates of 1, 2 or 3°C/min. Response surface methodology was used to create models of chromatographic efficiency as a function of temperature rate and carrier gas velocity. The chromatographic efficiency was defined as the inverse of peak widths measured in retention index units. The final results were standardized so that the efficiencies that could be achieved within a certain time frame, defined by the retention time of the last compound in the chromatogram, could be compared. The results show that there were clear differences in the efficiencies that could be achieved with the different columns and that the efficiency decreased with increasing polarity of the stationary phase. The differences can be explained by higher resistance to mass transfer in the stationary phase in the most polar columns.     

Analysis of fatty acids from human lipids by gas chromatography

A rapid, quantitative method is described for the analysis of fatty acids from human lipids, namely serum lipids and lipids from adipose tissue biopsies. The method includes extraction of serum lipids with chloroform--methanol, hydrolysis with tetramethylammonium hydroxide, methylation with methyl iodide and N,N-dimethylformamide and gas chromatographic analysis on a Supelcoport SP-2320 column. Fat biopsies are analysed without extraction. Optimal hydrolysis conditions have been investigated.     

Rapid identification of fatty acid methyl esters using a multidimensional gas chromatography-mass spectrometry database

A multidimensional approach for the identification of fatty acid methyl esters (FAME) based on GC/MS analysis is described. Mass spectra and retention data of more than 130 FAME from various sources (chain lengths in the range from 4 to 24 carbon atoms) were collected in a database. Hints for the interpretation of FAME mass spectra are given and relevant diagnostic marker ions are deduced indicating specific groups of fatty acids. To verify the identity of single species and to ensure an optimized chromatographic resolution, the database was compiled with retention data libraries acquired on columns of different polarity (HP-5, DB-23, and HP-88). For a combined use of mass spectra and retention data standardized methods of measurement for each of these columns are required. Such master methods were developed and always applied under the conditions of retention time locking (RTL) which allowed an excellent reproducibility and comparability of absolute retention times. Moreover, as a relative retention index system, equivalent chain lengths (ECL) of FAME were determined by linear interpolation. To compare and to predict ECL values by means of structural features, fractional chain lengths (FCL) were calculated and fitted as well. As shown in an example, the use of retention data and mass spectral information together in a database search leads to an improved and reliable identification of FAME (including positional and geometrical isomers) without further derivatizations.     

Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography

This paper describes novel and rapid thin-layer chromatography procedures for the analysis of fatty acids and methyl esters using silver-impregnated alumina sheets. These techniques are known in most laboratories, and the equipment is readily available. The fatty acid method allows a separation of petroselinic (C18:1 delta 6c), oleic (C18:1 delta 9c), elaidic (C18:1 delta 9t), erucic (C22:1 delta 13c), and brassidic acids (C22:1 delta 13t), and the methyl ester method gives an excellent resolution with respect to the number, configuration, and position of the unsaturated centers. Sufficient separation for the subsequent ozonolysis and chromatographic quantification of isomeric C18 and C22 fatty acid methyl esters is obtained with both methods.