Influence of adsorption effects on retention indices of selected C10-hydroxy compounds at various temperatures

Summary Retention indices of 6 selected hydroxy compounds (aliphatic and bicyclic alcohols, phenols) were determined on 2 HP-5 fused-silica, capillary columns with different film thicknesses (0.11 m and 0.33 m) at 8 different oven temperatures between 80 and 150°C. For some substances the I-T plot was found to show a minimum which cannot be explained by the common retention-index temperature-dependence in gas-liquid chromatography. This result is discussed in terms of adsorption at the liquid-solid interface of the capillary column.     

Characterization and purification of fatty acid methyl esters from the liver oil of the deep sea shark (Centrophorus squamosus) by gas chromatography-mass spectrometry and countercurrent chromatography

Summary In the course of our studies on the location of marine products, we have directed our attention to the saponifiable fraction of the liver oil from the deep sea shark (Centrophorus squamosus). Different analytical and preparative techniques, such as high-performance liquid chromatography (HPLC), countercurrent chromatography (CCC), and gas chromatography-mass spectrometry [GC-MS, electron impact (EI) and positive-ion chemical ionization (PCI)] were used. These methods allowed us to characterize, after various derivatizations, most of the fatty acids formed after the saponification of the oil, and to purify two of them, namely: docosahexaenoic acid (DHA or 226) and docosamonoenoic acid (DMA or 221).     

Prediction of the retention indices of methyl pyridines and pyrazines in capillary gas chromatography based on the non-linear additivity of the sorption energy

Summary Methylbenzenes, pyridines and pyrazines were investigated on fused-silica and glass capillary columns coated with SE-30 and PEG-40M/KF liquid phases, at two temperatures, 80° and 110°C. The contribution of the methylene groups to the partial molar free sorption energy was determined for methylpyridines and pyrazines. Equations are proposed for the calculation of the retention indices of methyl pyridines and pyrazines. These equations are based on the ortho- and α-effects of the methyl groups. The predicted indices have been experimentally tested for six dimethyl- and trimethylpyridines, and four methylpyrazines. Good accuracy of the calculation permits to use this method for the identification of methylpyridines and pyrazines in complex mixtures. Enlarged text of the paper presented at the Eighth International Symposium on Capillary Chromatography, Riva del Garda, Italy, May 19–21, 1987.     

At-column injector for capillary GC — design and evaluation

The present paper describes constructional details and evaluations of an at-column injector for capillary GC. Injections were made via a sample loop on a 0.32 mm i.d. capillary column. Two rotary valves were employed to allow a wash of the sample loop and a backflush of the transfer line. Repeatability, calculated from absolute area counts for n-alkanes was between 0.3–1% RSD, for injected sample volumes between 5 and 100 μl. Promising results were also obtained with syringe-based injections on narrow bore (100 μ i.d.) columns. Repeatability on the basis of normalized area counts was in the order of 0.1–0.2% RSD, while solvent tailing was practically absent.     

Gas-chromatographische Bestimmung von Glykokollbetain in Mischfuttermitteln

Zusammenfassung Es wird eine Methode zur gas-chromatographischen Bestimmung von Glykokollbetain in Mischfuttermitteln beschrieben. Die Extraktion erfolgt mit Alkohol, anschließend wird die Lösung über einen Kationenaustauscher gereinigt. Das Betain wird mit N-O-Bis-(trimethylsilyl)-trifluoracetamid und Acetonitril verestert und gas-chromatographisch bestimmt. Für die beschriebene Methode errechnete sich bei einem Mittelwert von 2309 ppm und 7 Parallelen ein Variationskoeffizient von 1,79%.

---

Gas-chromatographic determination of glycocoll betaine in feeding-stuffs

The betaine is extracted with ethanol, purified by cation-exchange chromatography, esterified with N-O-bis-trimethylsilyl-trifluoracetamide and determined by gas chromatography. The coefficient of variation for the described method for 7 parallels and an average of 2309 ppm was 1.79%.

     

Characterization of OV-1/FFAP-mixture coated glass capillary columns used for the separation of free fatty acids

As an alternative to acid pretreated UCON and FFAP capillaries for the analysis of wide-boiling free fatty acid mixtures, OV-1 : FFAP phase mixtures were used on high-temperature silylated inert glass capillary columns. The HETP-carrier gas velocity curves, peak asymmetry factors, coating efficiency, gas phase and stationary phase contributions to the mass transfer resistance were determined for various OV-1 : FFAP ratios. Mixed-phase capillaries showed optimum performance at a 2 : 1 OV-1 : FFAP ratio. The thermal and long-term stability of OV-1-stabilized FFAP columns surpassed those of the UCON and pure FFAP reference column used.     

Isolation of essential oils from tobacco by gas co-distillation/solvent extraction

Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

Influence of some inorganic salts on the polarity of apolar polymer phases in capillary gas chromatography

Different stationary phases were prepared by mixing a series of inorganic salts with dimethylsiloxane polymer (SE-30) and then tested by capillary gas chromatography. It was demonstrated that the polarity (as evaluated by measurement of Rohrschneider constants) of the mixed stationary phases, which is inferior or equal to that of a medium-polar OV-25 phases, reached even lower values than SE-30 alone. The influence of NaF, NaCl, NaBr, AgNO₃, and other inorganic salts on the polarity of capillaries is reflected by a better resolution and shorter retention time of cis/trans isomers of fatty acid methyl esters (FAMES) as well as positional isomers of triglycerides.     

Glass capillary gas chromatography of amino acid enantiomers

Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable.