Temperature dependence of the resolution of diastereomeric isoprenoids in capillary GC. Experiments with 50 μm, 100 μm,and 250 μm i.d. Columns

The resolution of the diastereoisomers of norpristane, pristane, and phytane was studied as a function of the column internal diameter and/or the residence time of the compounds in the column. Increasing the residence time in the column by operating the column at a lower temperature program rate enhances the resolution more than reducing the internal diameter of the column. Practical experience with ultra narrow bore columns is also presented.     

Fused silica capillary micro-packed columns in gas chromatography

Summary Flexibility, strength and adsorption inertness of fused-silica capillaries permits their extensive application for the preparation of micro-packed columns in gas chromatography. Decreasing the column diameter (from 0.5 to 0.15 mm) and the diameter of the sorbent particles (from 100 to 5 μm) results in a marked reduction of the height equivalent to a theoretical plate (HETP), as well as in diminishing the dependence of the HETP on the carrier gas flow rate. The chromatographic characteristics of fused-silica capillary micro-packed columns and open-tubular columns are compared. The fused-silica capillary micro-packed column can be used to advantage for performing rapid and trace analyses and have been shown to be adapted for application in gas-solid chromatography. Separation of organic and inorganic compounds on fused-silica capillary micro-packed columns is illustrated by practical examples. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

A study of some deactivation methods for fused silica capillary columns by CP-MAS NMR and capillary gas chromatography

The effect of deactivating a fused silica surface by silylation with 1,1,3,3-tetraphenyl-1,3-dimethylilazane (TPDMDS), triphenylsilylamine (TPSA), and octamethylcyclotetrasiloxane (D4) and by polydimethylsiloxane degradation (PSD) is studied. Rehydrated, dried, and deactivated Cab-O-Sil M5 samples are used as model materials for ²⁹Si CP-MAS NMR analysis. At about 350 °C, TPDMDS yelds mainly diphenylmethylsiloxysilane, dimethyldisiloxysilane, and triphenylsiloxysilane groups. TPSA yields phenyltrisiloxysilane, diphenyldisiloxysilane, and triphenylsiloxysilane groups. At 400°C, the products formed initially are eventually replaced by methyltrisiloxysilane or phenyltrisiloxysilane groups, while a substantial number of silanol groups still remains. The possible consequences for wettability are discussed. D4 reacts with Cab-O-Sil even at 200°C, but a large number of silanol groups remains. This number decreases gradually at higher temperatures and becomes negligible above 400°C. The formation of methyltrisiloxysilane groups, which starts at 425°C, is predominant at 490°C.     

Automated at-column injection into narrow bore capillary GC columns

An injector designed for automatic direct liquid injection into narrow bore capillary GC columns has been constructed and evaluated. The tip of the syringe needle is aligned with, and positioned close to, the column entrance in a small, pressurized cavity: when the sample is dispensed it is immediately forced into the column by the action of the surrounding carrier gas. A standard autosampler equipped with a standard stainless steel syringe needle was utilized for at-column sample transfer into 100 μm i.d. columns. RSD values for n-alkanes were between 0.1 and 0.3% for relative area counts and approximately 1% for absolute area counts.     

Some applications of capillary gas chromatography in the chemical industry

About three years ago, fused silica capillary columns were introduced in the Quality Control Laboratory of the Shell refinery/chemical complex at Pernis. In general, long, thick-film, wide-bore capillary columns are used together with low split ratios and hydrogen as carrier gas. These conditions enable the analysis of relatively large sample amounts, resulting in low detection limits for the minor components without overloading by the major components, while still maintaining a satisfactory resolution. A number of applications are shown, such as the analysis of complex mixtures, the determination of trace impurities and the analysis of residual volatiles in polymers.     

Construction and application of a cold on-column injection system for capillary gas chromatography

A cold on-column injection system for capillary gas chromatography (GC) applications was constructed. It was based upon a conventional split/splitless capillary GC inlet, which in turn was a modification of a conventional packed GC column inlet. The heart of the laboratory constructed cold on-column inlet design was a disposable pyrex micro-sampling pipet, which functioned as a needle guide for sample injection. The sample was injected through a traditional GC septum. Construction of the injection system is described and applications are illustrated by separations of a variety of complex mixtures.     

High temperature gas chromatography on narrow bore capillary columns

The use of high-temperature-stable, medium polarity glass capillary columns coated with immobilized PS-090 (a 20 % diphenyl-substituted, CH₃O-terminated polydimethylsiloxane) has made it possible to analyze routinely, and with good separation efficiency, high molecular weight compounds such as triglycerides and free base porphyrins. Cold on-column injection was used throughout this work to avoid discrimination against involatile compounds, and disposable (fused silica) retention gaps were used to protect the column against contamination with involatile material. On-column injection into narrow bore glass columns was achieved by using glass-to-silica connections to attach wider bore (0.2 mm i.d.) deactivated fused silica tubing to the columns.     

Enzyme activity determination by radio gas chromatography on capillary columns

Androgen 5α-reductase from the foreskin of 48 boys in prepubertal age was analyzed by evaluation of the apparent K_m-and V_max- values after tissue incubation. Reaction rates were calculated after determination of specific radioactivity of distinct metabolites, by comparison to the radioactivity of the precursor. Reaction products were separated by radio gas chromatography on capillary columns. The chromatography system was based on multicolumn equipment with column switching facilities and a variable splitter at the outlet of the separation column. A radioactivity monitor (gas proportional counter) was used for measurement of radioactivity in the column effluents. An electron capture detector was used for mass detection of steroid acyl derivatives.     

Narrow bore silica capillary columns for liquid-modified adsorption gas chromatography

Summary The preparation of narrow bore capillary columns for liquid-modified adsorption chromatography is described, and the advantages of this technique for rapid analysis of complex mixtures are discussed.Several applications to the analysis of complex mixtures are reported, and the possibility of on-column injection is demonstrated.     

Determination of amino acids by gas chromatography using a wide bore capillary column

A procedure is described in which a wide bore capillary column is used as an alternative to the more traditional packed column for the quantitative analysis of amino acids as their N-heptafluorobutyryl isobutyl ester (HBB) derivatives. The column, installed in a gas chromatograph previously configured for use with a packed column, is shown to give good reproducibility by repeated determination of amino acid response factors (RSD values for all amino acids are below 3%). A number of problems, encountered during the use of this column, are discussed and suitable techniques to overcome them are reported.     

Deactivation of fused silica capillary columns with phenylhydrosiloxanes

In this work, an investigation of new organosilicon hydride reagents with phenyl functional groups for deactivation and surface modification of fused silica capillary columns is described. Different reagents were tested for their ability to deactivate the fused silica surface, and actual critical surface tension measurements were made using the capillary rise method. The deactivation procedure required lower optimum temperatures than conventional methods. Deactivated capillaries and coated capillary columns were prepared and tested for reproducibility, efficiency, and surface inertness towards basic and acidic compounds at the low nanogram level.     

A CP-MAS NMR study of some deactivation methods in capillary gas chromatography

The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by ²⁹Si and ¹³C CP-MAS NMR. Fumed silica (Cab-O-Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material. Hexamethyldisilazane (HMDS) and 1,2-diphenyl-1,1,3,3-tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl- and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The ¹³C NMR and GC-MS of the reaction products showed that with DPTMDS, the formation of two Si-O-Si links is accompanied by a loss of phenyl groups rather than of methyl groups. After the Cab-O-Sil had been dried over P₂O₅, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si-O-Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.     

Gas chromatography of plasma amino acids using a wide bore column: Comparison with packed and capillary columns

A procedure is described in which a wide bore glass capillary column is used as an alternative to the more traditional packed column in the analysis of amino acid levels in plasma. The coefficients of variation for all amino acids (with the exception of aspartic acid) were better than 11% with recoveries ranging from 81% to 122%. The data are compared with the corresponding results obtained using a packed column and show significant differences (p < 0.005) between values for glycine, serine, isoleucine, proline, methionine, aspartic acid, phenylalanine, and lysine. A similar comparison between results from the wide bore and the fused-silica open tubular (FSOT) column shows better agreement. Adjustment of chromatographic conditions for the wide bore analysis yields results in good agreement with those from FSOT analysis but which still differe significantly from the backed column data.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

Separation of mixtures of solvents with wide bore capillary columns connected in series

The gas chromatographic separation of the components of a complex mixture of industrial solvents, not possible on a single stationary phase owing to coelution of some of the compounds, has been achieved on two serially connected wide bore capillary columns of different polarity. The analysis of a mixture of twenty five compounds was optimized using the serial gas chromatography theory of Purnell and Williams. The capacity factors of sample components measured with the two columns coupled in series were found to agree with those predicted by theory, regardless of the order in which they were connected.