Direct injection on capillary columns for gas chromatography

Discrimination may occur when injecting samples onto gas chromatography capillary columns, whereby peak areas for higher boiling point compounds are smaller than they should be compared to lower boiling compounds. This problem is most important in quantitative work on solutes having a wide range of volatility. An all-glass inlet system was used. Injections were made with a 10-μl syringe onto a column without and injection point heater and with the column oven about 20°C below the boiling point of the solvent used for the solutes. Discrimination did not occur in a range of C₁₂ to C₃₆ n-alkanes.     

Performance of capillary columns for high-temperature gas chromatography

The developments in stationary-phase synthesis and capillary column technology have opened new perspectives in the analysis of high-molecular-weight compounds (600 daltons) and thermolabile organic compounds by high-temperature-high-resolution gas chromatography. This branch of high-resolution gas chromatography deals with analysis performed up to 390 degrees C oven temperature (with some applications going up to 420 degrees C and even a few applications to 450 degrees C maximum). The technique has been applied to many different fields of science (e.g., organic geochemistry, environmental chemistry, archeology, and natural product research). Apolar and medium-polar gum phases can now be operated at temperatures from 400 to 480 degrees C, but these higher temperatures are seldom used because of the thermostability of the material used to make the capillary tubing. This paper shows the performance of nine commercial high-temperature columns when used in routine applications.     

Preparative gas chromatography with glass capillary columns

The present paper describes an automated system for preparative gas chromatography with glass capillary columns, controlled by a microprocessor. The effluent from the capillary column is divided by a pneumatically controlled splitter and any desired split ratio between traps and detector can be obtained. Moreover, a second pneumatic control allows instantaneous change-over to a different split ratio, thus minimizing loss of material during collection. The effluent containing the compounds of interest is passed through a multiple manifold and collected in coiled glass capillary traps. To ensure maximum trapping efficiency even for very small amounts of material, the inner walls of the capillary traps are wetted with a suitable solvent, which gives a quantitative recovery of micro- and nanogram amounts of material. After repetitive sampling, sufficient amounts of material can be obtained for NMR spectroscopy and possibilities exist to enrich trace components with the aid of a double column system. Two examples of such applications are given, employing mixtures of both synthetic and natural origin.     

Pulse circulation gas chromatography on capillary columns

The method and equipment for pulse circulation high-resolution gas chromatography on glass capillary columns have been developed. The separation of a mixture of C(6)H(6), C(6)H(5)D, C(6)H(3)D(3) and C(6) D(6) on carbonized columns coated with squalane has been taken as an example to show the advantages of the method. An efficiency of about 5 x 10(6) theoretical plates has been achieved with a capacity factor of k = 1.     

Stainless steel capillary columns for high temperature gas chromatography

A layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross-linked, silanol-terminated polydime-thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns.     

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     

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.     

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.     

Loading capacities of monolithic capillary columns in gas chromatography

The loading capacities of monolithic capillary columns based on silica gel and divinylbenzene are studied for two carrier gases, CO₂ and N₂. It is shown that the efficiency of the column is more sensitive to the overload of the column than the retention time of the sorbate is, especially for the CO₂ carrier gas. It is established that the loading capacity of a monolithic column based on silica gel decreases significantly in going from N₂ to CO₂. For columns based on divinylbenzene, the loading capacity is found to be virtually the same for both carrier gases. For monolithic columns, the loading capacity per one meter of column length is found to be 10 and more times higher than that for a standard open capillary column.     

Efficiency of monolithic capillary columns in high-pressure gas chromatography

Monolithic sorbents for gas chromatography obtained in quartz capillaries are analyzed by means of kinetic curves (Poppe plots). The values for the time of a theoretical plate and the maximum number of plates are found to be strongly dependendent on the parameters of monolith synthesis, i.e., the relative amount of a monomer in the initial mixture, the temperature, and the polymerization time. Synthesis conditions are established using the kinetic curves, allowing the preparation of sorbents suitable for both performing high-rate analysis and achieving the most effective separation. It was shown that plotting kinetic curves on the basis of van Deemter curve data requires we allow for the compressibility of mobile phase.     

Packed capillary columns for liquid chromatography

Summary Fused silica capillaries, ≈ 130 × 0.32mm have been packed with small reversed phase spherical silica particles, 3 or 2μm, in order to achieve LC-systems giving high plate numbers at relatively low pressure drop in short analysis times. At optimal conditions, columns packed with 3μm particles showed reduced plate heights, h, around 2.5, and the column flow resistance, ϕ, was 335–625. With 2μm particles, a reduced plate height of only 3.7 was achieved, which reflects the difficulty in the packing of such small particles.     

Wide-bore glass capillary columns for gas chromatography. Their preparation and application

Summary Methods for the preparation of wide-bore glass capillary columns for gas chromatography are presented. The pretreatment of the columns (etching, carbonization, deactivation and/or surface-coating with porous materials), and the coating of them with polar or apolar phases (preferably by the static method) is described. The performance of the columns prepared is evaluated and a number of applications are given, such as analysis of volatile compounds, pesticides, lipids and GC/MS analysis. In some respects, the wide-bore glass capillaries have advantages over the narrow-bore types. They can be installed very easily in GC-instruments, and permit the analysis of larger samples. A system of collecting separated sub-g fractions in glass capillary traps, which makes direc re-injection from these traps possible, completes the methods presented.     

Deactivation of small-diameter fused-silica capillary columns for gas and supercritical fluid chromatography

Summary In order to prevent plugging during deactivation of small diameter (50 m i.d.) capillary columns for gas and supercritical fluid chromatography, various high temperature deactivation methods were employed. Pure hexamethyldisilazane and hexamethyldisiloxane (a substitute for D₄) were dynamically coated on the column, while a film (0.05 m) of OV-101 was statically coated, before high temperature (450°C) treatment. Excellent deactivated columns were obtained, and no significant difference in column activity was observed using any of these three methods.Dedicated to Professor S. R. Lipsky on the occasion of his 60th birthday.     

Chromatographic peak broadening in circulation gas chromatography on capillary columns

Conclusions Ideas about the effect of the hydrodynamic pulse broadening of Chromatographic peaks have been developed. The pulse peak broadening factor of compounds undergoing chromatography has been introduced to account for the effect of the partition ratio k, and the relationship of this new factor to one proposed earlier has been established. The physicochemical concepts developed in the course of the theoretical investigations are supported by experimental results for circulating gas chromatography on glass capillary columns.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2019–2024, September, 1986.