Gas-liquid Chromatographic Separation Research Articles

Flame‐ionization detector response to methyl, ethyl, propyl, and butyl esters of fatty acids

AbstractThe concept of theoretical response factors is not directly applicable to methyl esters of short‐chain fatty acids (FA), since their carbon deficiency is larger than expected from theory. Substituting the methyl group by an ethyl, propyl, or butyl group improved the flame‐ionization efficiency of fatty acid esters gradually, up to the point where the empirical response factors of the butyl esters were identical within experimental error to the theoretical values. Butyl esters of FA have a uniform flame‐ionization detection (FID) response irrespective of the number of carbon atoms contained in the FA. They exhibit a carbon deficiency of 1.0, i.e. the carbonyl carbon atom does not respond, as expected from theory. Compared to methyl esters, which have a carbon deficiency of 1.4–1.5 for short‐chain FA, use of butyl esters has the advantage that a precalculation of the FID response enables the analyst to judge whether the analytical system employed works properly and the data produced are accurate and reliable. Both acid (BF3 or H2SO4)‐and alkali (butoxide)‐catalyzed butyl ester preparation were equally effective, giving the analyst a choice of methods so that different analytical needs can be addressed efficiently. Computing response factors and comparing the theoretically expected values with those obtained experimentally gives the experimenter an indication whether the analytical system employed for FA profiling (transesterification plus the subsequent gasliquid chromatographic separation and quantitation by FID) works properly. This setup is particularly useful for an accurate analysis of the FA profile of milk fat.

Capillary column gas–liquid chromatographic separation of Δ5-unsaturated and saturated phytosterols

Diets consisting of food ingredients of both plant and animal origin contain a complex mixture of sterols in the lipid fraction. Analysis of these complex mixtures of sterols is generally accomplished by capillary column GC and GC–MS. A very low polarity liquid phase (methylsilicone) and medium polarity columns of various dimensions are used for the separation and quantitation of sterols. However, these columns may not be able to separate some of the sterols in the mixture. The objective of this study was to accomplish the complete separation of a complex mixture of sterols by GC. In order to achieve this objective, a fused-silica capillary column (14% cyanopropyl-phenyl-methylpolysiloxane) of low/medium polarity was used. Excellent separation of campesterol and campestanol, and sitosterol, sitostanol and Δ5-avenasterol was achieved. In addition to GC resolution, a few critical points for the analysis of sterols are presented.

Direct Measurement of Total trans- and cis-Octadecenoic Fatty Acids Based on a Gas--Liquid Chromatographic Class Separation of trans-18:1 and cis-18:1 Fatty Acid Methyl Esters

A gas-liquid chromatographic (GLC) class separation is described whereby the contents of total trans- and cis-octadecenoic fatty acids can be obtained for relatively simple samples such as margarines and for more complicated food mixtures and biological specimens. The method is an adjunct to the standard process commonly used for quantitating the general fatty acid profile of a sample (extraction of lipids, preparation of methyl ester derivatives of fatty acids, GLC separation on Carbowax-20M capillary columns). There is no incremental work beyond the addition of one chromatographic run on a cyanosilicone capillary column at 242°C that lasts only 20-25 min. The chromatograms provide a composite trans peak and a composite cis peak with sufficient resolution between them to provide direct estimation of total trans- and cis-octadecenoic fatty acids. A concurrent analysis for the general profile of fatty acids in an unknown (using Carbowax20M columns) is included with every analysis for trans content to check for internal consistency and for general quality control.

Simulation of the combined continuous and preparative gas-liquid chromatographic separation of three close-boiling components

A combined continuous and preparative gas-liquid chromatographic system was considered for separating continuously three close-boiling components, diethyl ether, dimethoxymethane and dichloromethane. Their concentration profiles were simulated by a mathematical model that assumed the uniform distribution of stationary liquid phase and linearity of the equilibrium isotherm. The operational principles of the system are that the least absorbed component of the three components can be obtained purely before the elution of the more absorbed components if the mixture is continuously injected into one of the two sections (partition section) and at the same time, in the other section (desorption section), the three components remaining in the column can be separated by adjusting the experimental conditions and the column configuration. If the operations in the two sections are simultaneously finished within the switching time, continuous separations of the three components are feasible. Effects of various operating conditions on the resolution were investigated. The results of the simulations indicated that the resolution was greatly affected by the additional column length in the desorption section and the switching time could be determined by the desorbent velocity.

Capillary gas-liquid chromatography of 6-hydroxylated bile acids

Gas-liquid chromatographic separation of several bile acids with a hydroxyl group at C-6 is described on two capillary columns, CP-Sil-19 CB and CP-Sil-5 CB. The gas-liquid chromatographic retention indices of bile acids with 6α- and 6β-hydroxyl groups are compared with those of bile acids without the C-6 hydroxyl group and the effect of the C-6 hydroxyl group on the retention indices of bile acids is determined. Both 6α- and 6β-hydroxyl groups increase the retention index of a bile acid. The retention indices of 6α- or 6β-hydroxyl derivatives of chenodeoxycholic acid were found to be higher than those of the corresponding 6-hydroxy derivatives of cholic acid on the CP-Sil-19 CB column but lower on the CP-Sil-5 CB column. Although all 6-hydroxylated derivatives of lithocholic, chenodeoxycholic and cholic acids were not completely resolved on either column alone, combining the two column resulted in the complete separation of all these compounds.

Capillary gas-liquid chromatographic separation of bile alcohols.

Gas-liquid chromatographic separation of C23, C24, C25, C26, and C27 bile alcohols with either 3 alpha, 7 alpha-dihydroxylated or 3 alpha, 7 alpha, 12 alpha-trihydroxylated ring system on two capillary columns, CP-Sil-19 CB and CP-Sil-5 CB, is described. Bile alcohols with two ring hydroxyl groups at 3 alpha- and 7 alpha-positions consistently showed larger retention times on CP-Sil-19 CB columns and smaller retention times on CP-Sil-5 CB columns than the corresponding bile alcohols with three ring hydroxyl groups at 3 alpha-, 7 alpha-, and 12 alpha-positions. Resolutions of all bile alcohols were better on CP-Sil-19 CB columns; however, we hope that the gas-liquid chromatographic characteristics on the two columns will be useful for better identification of bile alcohols in biological fluids.

Determination of hydrogen peroxide in fish products and noodles (Japanese) by gas-liquid chromatography with electron-capture detection

A sensitive and practical method for the determination of hydrogen peroxide (H2O2) in various fish products and noodles (Japanese) is described. The method is based on the gas chromatographic measurement of 2-hydroxyanisole, as its pentafluorobenzoyl (PFB) derivative, which is a product of the hydroxylation of anisole by reaction with H2O2 and potassium hexacyanoferrate(III) [K3Fe(CN)6] in the acid solution. The PFB derivative of 2-hydroxyanisole is determined by gas-liquid chromatographic separation on a 5% OV-17, 5% OV-210 mixed-phased column using an electron-capture detector (GLC-ECD). The calibration curve for H2O2 in the range 0.1-1.0 micrograms/mL is linear and sufficiently reproducible for quantitative determination; the detection limit for H2O2 is 0.06 micrograms/mL of sample extract. The coefficient of variation (n = 5) of the values determined is below 4.9%, and the average recovery rate throughout the procedure, including derivatization and gas-liquid chromatography, was above 87.1% in the fish products and noodles investigated. Although various possible metal ions and organic substances in the samples to be analyzed were tested at relatively high levels, all of them did not interfere with the production of 2-hydroxyanisole. The derivatization process was simple and rapid, requiring about 60 min, and the resulting derivative was stable for at least 1 week if stored under appropriate conditions.

Determination of sulphur compounds in Iraqi natural gasoline

Characterization of sulphur constituents of natural gasoline was performed using chemical methods of abstraction of sulphur containing groups, followed by gas liquid Chromatographic separation with flame photometric detection for the determination of individual sulphur compounds. Three thiols and fourteen disulphides have been identified.

Analyzing normetabolites of the fentanyls by gas chromatography/electron capture detection.

A selective and sensitive gas-liquid chromatographic (GC) method has been developed for analyzing the normetabolites of fentanyl and 3-methylfentanyl in urine. The method employs differential pH extraction of 1 mL samples, extractive acylation with pentafluoropropionic anhydride (PFPA), GC separation on a fused-silica capillary column (DB-1701), and detection by electron capture detector (ECD) or mass spectroscopy (MS). Limit of sensitivity for this method is 2 ng/mL for norfentanyl (NF) and nor-3-methylfentanyl (N-3-MF) using a 1-mL urine sample and a 2-microL injection from a final volume of 20 microL. Within-run precision, expressed as the coefficient of variation (CV), was 14% and 5% for 4 ng/mL and 16 ng/mL of NF and 9% and 4% for the same concentrations of N-3-MF. Between-run precision was 30% and 12% for NF and 11% and 10% for N-3-MF, at 4 ng/mL and 16 ng/mL, respectively. Metabolites are stable in urine for at least one month at room temperature (25 degrees C) or -20 degrees C. PFP-derivatives of the metabolites were confirmed by high-resolution MS in the electron-impact mode. Three characteristic ions for each metabolite were identified-m/z 392 (molecular ion), m/z 336 (loss of propionyl), and m/z 244 (loss of propionanilide) for N-3-MF-PFP and m/z 378 (molecular ion), m/z 322 (loss of propionyl), and m/z 230 (loss of propionanilide) for NF-PFP, suitable for use in GC/MS with selected ion monitoring as a complimentary confirming technique. This method was validated by analyzing urine samples from individuals suspected of using fentanyl or 3-methylfentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas Chromatographic Separation of Zirconium and Hafnium

Zirconium and hafnium present one of the most difficult chromatographic separation problems. This paper reports the first successful gas-liquid chromatographic separation of these elements using volatile metal chelates prepared via the direct reaction of 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione with the anhydrous halides in CCl4.

Effect of growth stage on mycolic acid structure in cell walls of Nocardia asteroides GUH-2.

Mycolic acids were extracted from the cell walls of Nocardia asteroides GUH-2 during different phases of growth at 37 degrees C. These were subjected to structural analysis by combining thin-layer chromatography and gas-liquid chromatography with UV and infrared spectrophotometry and mass spectroscopy of both methyl esters and trimethyl silyl derivatives. By analyzing the fragmentation patterns of these derivatives by three different methods of mass spectroscopy combined with gas-liquid chromatographic separation, the different structural subclasses of mycolic acids were quantitated. Significant qualitative and quantitative modifications of specific mycolic acid subclasses occurred in the cell walls of N. asteroides GUH-2 that were growth stage dependent. The mycolic acids that were predominant in the log phase were polyunsaturated (greater than 2 double bonds per molecule), with long chain lengths and even carbon atom numbers (i.e., C54, C56). In contrast, those that were prominent in the stationary phase were more saturated (few or no double bonds) and of shorter overall carbon chain length (less than or equal to C52). Furthermore, stationary-phase cells had significantly increased amounts of mycolic acids with odd-numbered carbon chain lengths (i.e., C49, C51, C53).

Heavy alkylated benzene stationary phase for the gas—liquid chromatographic separation of light hydrocarbons

Heavy alkylated benzene stationary phase for the gas—liquid chromatographic separation of light hydrocarbons

Gas-liquid chromatographic separation of aldose enantiomers as trimethylsilyl ethers of methyl 2-(polyhydroxyalkyl)-thiazolidine-4(R)-carboxylates.

Pairs of enantiomers of nine aldoses were separated by gas-liquid chromatography on an OV-17 capillary column as the trimethylsilyl ethers of methyl 2- (polyhydroxyalkyl) -thiazolidine-4 (R) -carboxylates, which were obtained by the reaction of aldoses with L-cysteine methyl ester. This method was applied to the determination of the absolute configurations of the component monosaccharides of a Thladiantha saponin.

Heavy alkylated benzene stationary phase for the gas-liquid chromatographic separation of ethylbenzene, xylenes, styrene, iso- and n-propylbenzene

Heavy alkylated benzene stationary phase for the gas-liquid chromatographic separation of ethylbenzene, xylenes, styrene, iso- and n-propylbenzene

Thin-layer chromatographic identification and gas-liquid chromatographic separation of seven aminobutyric acids in the presence of protein and non-protein amino acids

Gas—liquid chromatographic separation of the following aminobutyric acids as their trifluoroacetyl n-propyl esters was achieved on 0.65% ethylene glycol adipate coated on a Chromosorb W AW: α-aminoisobutyric; α-aminobutyric; β-aminoisobutyric; β-aminobutyric γ-aminobutyric; γ-amino-β-hydroxybutyric and diaminobutyric acid. Only the two isomers of 3-aminobutyrate were not completely separated. Additionally, the positions of the aminobutyric acids and some other amino acids occurring in bacterial fermentation broths on a cellulose thin-layer plate after two-dimensional separation are given. In the fermentation broth of Clostridium oncolyticum M 55, only α-aminobutyric and γ-aminobutyric acid were identified as excretion products. In addition to these, Clostridium sporogenes produced additionally β-aminobutyric acid in quantities equalling γ-aminobutyric acid production. α-Aminoisobutyric and β-aminoisobutyric acid were completely absent, and γ-amino-β-hydroxybutyric and diaminobutyric acid were detected in low concentrations throughout the entire fermentation.

Gas liquid chromatographic separation of enantiomers as their diastereomeric derivatives, illustrated with 2-methylbutyric acid

A gas—liquid chromatographic method has been developed to separate on a small scale (acid samples as small as 2 mg) the enantiomers of 2-methylbutyric acid and to estimate a few per cent of one isomer as a contaminant in the other. Both the α-methylbenzyl ester and the α-methylbenzyl amide give a satisfactory resolution of the enantiomers. Chromatographic conditions in the order of importance are the final column temperature, the rate of temperature programming and the initial column temperature.

Optimization of stationary phase selectivity for the gas-liquid chromatographic separation of C 8 cyclic and aromatic hydrocarbons using squalane and liquid crystal glass capillary columns in series

A procedure is described for the computer optimization of the selectivity of capillary columns in series for the gas chromatographic separation of cyclic and aromatic hydrocarbons. The selectivity of two columns in series is given by the column length fraction: x b  L B/( L A + L B), where L is the column length and A and B denote a non-polar stationary phase (squalane) and a polar stationary phase (liquid crystal), respectively. Columns of various lengths were coupled in series using shrinkable PTFE tubing. The optimization criterion used was derived from the Kováts retention indices of the solutes. At the optimum column selectivity few peak pairs were not resolved.

Thin-layer and gas-liquid chromatographic separation of trihydroxy pentacyclic triterpene alcohols from Calendula officinalis flowers

Thin-layer and gas-liquid chromatographic separation of trihydroxy pentacyclic triterpene alcohols from Calendula officinalis flowers

A quantitative determination by capillary gas-liquid chromatography of neutral and amino sugars (as O-methyloxime acetates), and a study on hydrolytic conditions for glycoproteins and polysaccharides in order to increase sugar recoveries

Complete gas-liquid chromatographic separation of O-methyloxime acetates ( syn and anti isomers) prepared from eight neutral sugars, three hexosamines, and muramic acid has been obtained, using a fused-silica Carbowax 20M capillary column. A single hydrolytic step for carbohydrate-containing biological material (≤2.5· 10 −3 m sugar solution in 4 n trifluoroacetic acid at 125°C for 1h) has been developed, and results have been compared with those obtained with standard hydrolytic conditions in order to ensure complete release of amino sugars from glycoproteins, together with minimum losses of neutral sugars. The combination of this acid hydrolysis with the above improved derivatization procedure for the gas-liquid chromatographic analysis has led to a simple, rapid, and sensitive analytical method, which has been successfully tested on three glycoproteins (fetuin, mucin, and peroxidase) and two plant cell-wall polysaccharide fractions (soluble fibers from carrots and soybeans).

Application of Liquid Crystals for Gas-Liquid Chromatography

Abstract A liquid crystalline homologous series of N-[4-(4-alkoxybenzoyloxy)benzylidene]-4-cyanoanilines was applied as a stationary liquid phase for the gas-liquid chromatographic separation of various positional isomers. It is shown that the nematic phase has higher selectivity for several positional isomers compared with the other mesomorphic phases.