High oven temperature — cold on-column injection for the automated CGC analysis of high molecular weight compounds such as triglycerides

Modification of the Carlo-Erba cold on-column injector for (automated) analysis of high molecular compounds at high oven temperature is described. The secondary cooling tube of the cold on-column injector is replaced by a lengthened tube through which a high air flow is directed. The injection site is maintained at 65–70 °C while the oven is at high temperature (? 300 °C). For automated injection, a short deactivated precolumn of 22 to 30 cm × 0.53 mm i.d. is coupled to the analytical column via a butt connector with make-up gas supply. For a triglyceride mixture, automatically injected at 300 °C, the mean % deviation for all peak areas was 1.8% and the mean % deviation for all retention times was 0.09 % for five consecutive runs.     

Determination of volatiles in spirits using combined stationary phases in capillary GC

Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1:1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.     

Capillary GC analysis of diesel fuels using simultaneous parallel triple detection

Diesel fuels from different parts of the UK have been analyzed for polycyclic aromatic hydrocarbons (PAH), nitrogen-containing PAH, and sulfur-containing PAH using capillary column GC with simultaneous parallel triple detection. The concentrations of polyaromatic compounds (PAC) were high and showed considerable variability amongst the fuels. The PAH are mainly naphthalene, fluorene, and phenanthrene and their alkylated homologs; the PANH are mainly carbazole and its methyl derivatives; the PASH are mainly dibenzothiophene and its methyl derivatives.     

Characterization,evaluation and in-situ cross-linking of new polar phases in capillary gas chromatography

Summary The possibilities of OV-1701 and RSL-310, two new stationary phases, have been evaluated for capillary gas chromatography in fused silica columns. OV-1701 is a cyanopropylphenyldimethyl polysiloxane of moderate polarity possessing excellent chromatographic characteristics. The phase exhibits high coating and chromatographic efficiencies, high temperature stability and is suitable for cross-linking. RSL-310 is a polar liquid stationary phase yet to be permanently bonded in a capillary column. The selectivity of both phases extends the applicability of fused silica columns.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Distribution of weight,density, and molecular weight in crude oil derived from computerized capillary GC analysis

Chromatographic separation of crude oil components has been performed on a 50 m Chrompack Sil 5 fused silica capillary column, temperature programmed from 10 to 300°C. Approximately 70 peaks eluting before n-nonane (n-C₉) and all normal paraffins to n-C₁₉ were identified by a retention time table. Peak areas were converted to weight % using 1-heptene as internal standard and relative response factors. Components were divided into boiling range groups from n-C₆ to n-C₁₉. Paraffinic, naphthenic, and aromatic distributions were obtained for the boiling point fractions up to n-C₉. Group average densities and molecular weights were calculated from pure component properties up to n-C₉. Knowing the density and molecular weight as functions of boiling range group to n-C₉, these functions can be extrapolated to n-C₁₉, based on data and correlations from more than 20 distillations of paraffinic North Sea oils adn condensates. The densities and molecular weights of the C₁₀+ and the C₂₀+ residues were calculated to satisfy a balance of weight, volume, and number of moles for the whole sample. Measurements on the residues were used to cross-evaluate the GC method against distillation. The difference in weight was estimated to be less than ± 0.5% in absolute terms for the C₁₀+ residue. The corresponding figure for C₂₀+ was ± 2%. Relatively, calculated densities are within ± 1%, molecular weights within ± 2% compared to direct measurements. Calculations were performed by a BASIC program in a GC interfaced computer.     

Anthracene silica gel,a new polycyclic-aromatic-bonded stationary phase for HPLC

Summary N(9-methylanthracene)aminopropyl silica gel is introduced as a new reversed-phase packing material. It has specific selectivity for some aromatic compounds. In this paper the anthracene phase is compared with commercial octadecyl-, phenyl- and aminopropyl-bonded silica gels.     

Capillary columns with immobilized stationary phases. Part 4: A moderately polar phase,OV-1701

Whereas the immobilization of apolar silicone phases is essentially understood and mastered, the corresponding treatment of even moderately polar phases remains problematical. Upon attack by peroxide radicals, these phases respond by forming active transformation products rather than by bonding to the support surface or to neighboring molecules. OV-1701 is at present the most polar stationary phase which can reasonably be immobilized. An essential feature of the practical procedure is the prevention of film breakage after coating the inert support surface and before immobilization. Two ways of overcoming this problem are presented.     

Synthesis and characterization of benzyl β-cyclodextrins used as GC stationary phases

Summary Heptakis(2,6-di-O-benzyl)-β-CD(I), heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD(II), heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD(III) and heptakis(2,6-di-O-benzyl-3-O-acetyl)-β-CD(IV) derivatives were synthesized and identified. Their thermal stabilities were tested using PyGC. These CD derivatives are stable up to 300°C and suitable for use as gas chromatographic stationary phases. The fused silica capillary columns coated with heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD and heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD showed excellent chromatographic properties in separating positional isomers.     

Preparation and characteristics of two new GC stationary phases-dihydroxy crown ether containing polysiloxane

Summary Two new kinds of crown ethers: 3,5-dibutyl-unsymmetrydibenzo-14-crown-4-dihydroxy (cis-, and trans-) with the OH-terminal silicone oil in different proportion were coated on glass capillary columns, and immobilized by condensation using a coupling agent of alkyltrimethoxysilane. Chromatographic characteristics, including column efficiency, polarity, selectivity, phase transition temperature and thermal stability were studied. The columns were compared with PEG-20M in terms of polarity and selectivity. The immobilization and retention mechanisms are also discussed.     

Rayleigh instability of stationary phase films in capillary column chromatography

The film of stationary phase on the wall of a capillary column and that of the phase solution during both static and dynamic coating is subject to Rayleigh instability, which is quite independent of so-called wettability. A theory is developed which shows that the logarithmic growth rate of Rayleigh instabilities is proportional to the surface tension and to the third power of the film thickness, and inversely to the viscosity and to the fourth power of the capillary diameter. Determination of the variation of the viscosities of stationary phase solutions with concentration in coating solvents, and the variation of the viscosities of neat stationary phases with temperature, both revealed that heating and/or diluting changed the viscosities of phases with π-electron-containing, groups much more than for polydimethylsiloxanes. Rayleigh instability is therefore more important during coating of phenyl-containing phases such as OV-17, and later during column operation. The efficiencies of capillary columns of different diameters coated with a number of phases under different conditions of temperature and coating rate, and then operated at different temperatures were in good agreement with the predictions of the theory.     

Capillary electrochromatographic separation of bovine milk proteins using a G-quartet DNA stationary phase

DNA oligonucleotides that form G-quartet structures were used as stationary phase reagents for separation of bovine milk proteins, including alpha-casein, beta-casein, kappa-casein, alpha-lactalbumin and beta-lactoglobulin. Both artificial protein mixtures and a skim milk sample were analyzed. The separations were performed using open-tubular capillary electrochromatography, in which the oligonucleotides were covalently attached to the inner surface of a fused-silica capillary. Better resolution was achieved using the G-quartet-coated capillaries than was achieved using either a bare capillary or a capillary coated with an oligonucleotide that does not form a G-quartet structure. A 4-plane G-quartet-forming stationary phase was able to resolve three peaks for alpha-casein and to detect thermal denaturation of the proteins in the milk sample. The results suggest that G-quartet stationary phases could be used to separate very similar protein structures, such as those arising from genetic variations or post-translational modifications.     

Analysis of mono-, di-, and triglycerides by capillary supercritical fluid chromatography

The separation of mixed mono-, di-, and triglycerides by capillary supercritical fluid chromatography is described. The separations were performed at low operating temperatures, using a carbon dioxide mobile phase, a conventional flame ionization detector, and two different stationary phases, DB-5 (95% dimethyl-(5%)-diphenylpolysiloxane) and DB-225 (50% cyanopropyl-methyl-(50%)-methylphenylpolysiloxane). Because the separations were performed at low operating temperatures, no thermal degradation of the glycerides was observed. Even under these mild operating conditions, trinervonin, a triglyceride having a molecular weight over 1100 amu, was readily eluted. When rapid pressure programming of the carbon dioxide mobile phase was employed, trinervonin was eluted in less than two minutes. On DB-5, the mono-, di-, and triglycerides eluted in order of increasing molecular weight. A graph of t′_r (on DB-5) versus molecular weight is linear. When DB-225 was used as the stationary phase, triglycerides eluted in the order of increasing unsaturation. Thus, the order of elution on DB-225 was tristearin, triolein, trilinolein, and trilinolenin.     

The use of glass and fused silica open tubular columns for the separation of structural,configurational, and optical isomers by selective complexation GC: Sec-alcohols and ketones

The use of glass and fused silica open tubular columns for selective separation of structural, configurational, and optical isomers (enantiomers) of underivatized aliphatic alcohols and ketones by complexation gas chromatography on optically active metal chelates is described. The method represents a powerful analytical tool for the precise determination of diastereomeric (d.e.) and enantiomeric (e.e.) excesses in asymmetric syntheses and in natural product characterization. The direct screening of the enantiomeric composition and absolute configuration of terpinene-4-ol, the aggregation phermone of Polygraphus poligraphus (L), is described.