GC with LC-like packed capillary columns

Capillary columns of 0.3–0.35 mm internal diameter and 0.3–7.7 m length, packed with 3 to 30 μm octadecylsilica stationary phases as used for liquid chromatography, were applied to gas chromatographic separation of low boiling hydrocarbons. Van Deemter plots for these columns showed the optimum column efficiency to occur at linear velocities of 4–5 cm/s. A short column was applied to the rapid separation of components of a natural gas and impurities in standard gases, while a long column was applied to the separation of complex mixtures.     

A technique for coating capillary columns with a very thick film of cross-linked stationary phase

A method for preparation of capillary columns and traps with a very thick film (up to 100 μm) of stationary phase is described. The principle of this method is based on an immediate fixation of a film of prepolymer, formed during dynamic coating. Thus, the development of film irregularities, such as are caused by Rayleigh instability is avoided. Fixation of the film is conveniently accomplished by heat-accelerated crosslinking as was demonstrated in this work, where a commercially available silicone prepolymer (Sylgard 184, Dow Corning) was employed. The low phase ratio columns which thus can be prepared are interesting both in chromatography with dense mobile phases and as enrichment devices. Examples of the latter application are shown, where trace organic components from air and water were concentrated.     

Toward rapid preparation of capillary columns for electrochromatography use

CEC is a high performance electrodriving liquid phase separation technique. It does not need complex and sophisticated high pressure instrumentation for nanoflow driving. This is attractive for parallel multicolumn analysis. To this end, high throughput methods for column preparation are needed to support the use of multiple columns. In this study, we directly used CEC mobile phase solution as the packing solvent, and realized rapid preparation of capillary columns based on a single particle fritting technology. The method presented high preparation throughput compared with other reported methods based on various fritting technologies. The single particle fritting approach promoted column preparation throughput to 1 column/h, including all the fritting, packing and conditioning steps. The rapidly prepared columns showed consistently high efficiency of up to 150 000 plates per meter, and usefulness in reversed phase CEC of neutral, charged and biomolecules. With standard peptides as the sample, excellent long term reproducibility (better than 0.8%RSD, ten days, for retention times) was observed.     

Dry-packed capillary columns for micro HPLC

A dry-packing method has been developed which enables the preparation of packed capillary columns for micro HPLC from 250 μm i.d. tubing and 5 μm packing materials. Pressurized gases, such as hydrogen and argon, were used to transport the packing media, and ethanol or methanol were used as discharge agents. By changing the gas pressure, the packing density could be easily adjusted. It was found that, within experimental limits, the higher the packing density, the greater the column efficiency. Comparison between dry- and slurrypacked columns showed that the former had greatly improved stability; the efficiency of dry-packed columns was about the same as, or even better than, that obtained by slurry-packing.     

Micropreparative system for enrichment of capillary GC effluents

An automated system for preparative gas chromatography with capillary columns is described. The effluet from the capillary column is switched to the FID detector or to the traps by means of a Live-T switching device. The pneumatics is controlled by a microprocessor so that repetitive sampling can be performed over a period of days in order to enrich sufficient amount of material for NMR or other spectroscopic methods. The effluent containing the compounds is collected in glass tubes filled with column packing material (e.g. Chromosorb coated with 3% OV - 101, crosslinked). The trap temperatue can be adjusted from + 20°C to ? 80°C, depending on the trapping material and volatility of trapped substances. The analysis of enriched substances or chromatographic fractions can be performed by thermal desorption of the same traps or by solven elution. The recovery of enriched substances is higher than 90%. High capacity and resolution for enrichment of trace components are obtained with the aid of a double column-double oven system. Examples of such applications are given.     

Microbore columns in quantitative column liquid chromatography

Summary Some quantitative implications of the use of microbore columns in column liquid chromatography are investigated. Although for several pumps the flow rate stability at 50 l min^–1 is slightly worse than that of pumps operating at 1 ml min^–1, the quantitative performance with respect to repeatability and reproducibility of response factors equals that of conventional liquid chromatography. Thermostatting is strongly recommended for microbore column operation.     

Some practical experiences in the use of a solventless injection system for packed column supercritical fluid chromatography

The operating characteristics of a solventless injector for packed column supercritical fluid chromatography are described. Successful operation depends on the difference between the volatilities of the analytes and the solvent or matrix being sufficient for their separation by gas purging in a thermostatted precolumn, and also on the existence of an effective re-focusing mechanism at the head of the analytical column for the sample dissolved in liquid or supercritical fluid carbon dioxide. The latter is easily achieved in density programmed operation by stationary phase trapping at low fluid densities or phase ratio trapping by changing the temperature at low to moderate fluid densities. The solventless injector can easily accommodate sample volumes from 1–100 μl and is easily adapted for in-line derivatization using reagents which can, after reaction, be eliminated by gas purging. For general purposes the solventless injector can be used to overcome most of the problems encountered when rotary valve loop injectors are used with small bore packed columns, and will probably replace this type of injector as the injector of choice for supercritical fluid chromatography with mobile phases of low polarity.     

Advances in two-dimensional GC with glass capillary columns

A versatile two-dimensional gas chromatograph is described, consisting of 2 separate ovens, one intermediate trap, an auxiliary inlet, and the necessary hardware to effect off-line switching according to the principle of Deans. The unit has been designed for use with high resolution glass capillary columns. The performance of individual instrumental components was critically evaluated. Results showed that low dead volume glass to metal connections were required in the manifold and detector lines to minimize extra-column effects. The mass of the intermediate trap must be low to allow rapid heating. Operational parameters are discussed and examples of some applications are shown.     

A new type of two-dimensional packed + capillary column GC system. I. Theory

Summary To match the need of high efficiency capillary column (plate number N₂, Plate height H₂ and carrier gas linear velocity U₂), a new high efficiency packed column (N₁, H₁ and U₁) at high carrier gas velocity with small capacity factor has been developed in the light of theoretical discussion of factors effecting the column efficiency utilization ratio.     

A versatile all-glass GC/MS interface for capillary columns

A new all-glass interface for GC/MS designed to fully exploit the potential of glass capillary columns is described. The system works in the open split mode and has high versatility with respect to column changing. It is especially suitable for mass spectrometers, which are not exclusively dedicated to GC/MS work. Two chromatograms illustrate the properties of the described interface.     

The use of silicon in the preparation of apolar glass capillary columns

As an extention of previous reports, variables affecting the performance of columns modified by silicon deposition have been optimized. The aim of this work was to produce thermostable apolar glass capillary columns regardless of the glass type used and to maintain column performance under stressful conditions. The main parameters studied were the influence of glass type, leaching effects, and silicon layer thickness on column activity. Deactivation and stationary phase conditions were held constant. Both coated and uncoated columns were tested. The thickness of the silicon layer was found to be relatively unimportant. There was no difference whether soft glass or borosiiicate glass was used and leaching before silicon deposition did not influence column activity. Bare silicon surfaces showed considerable activity especially in respect to interactions with free acids and bases. There are indications that the surface consists of silicon oxide and other oxygenated forms of silicon rather than of the element. Treatment of the silicon layers with dilute hydrofluoric acid and the strict exclusion of traces of oxygen and water did not improve the situation. In spite of such specific interactions, silicon surfaces were easily deactivated by heat treatment with polysiloxanes. Silicon surfaces deactivated by baking with octamethyltetrasiloxane at 400°C are inert and temperature stable and show characteristics similar to persilylated surfaces.     

Advances in the preparation and evaluation of GC capillary columns

The preparation of (glass) capillary columns of high quality is still not without difficulties. Six problems in this context are highlighted. Column material choice(l), glass wall modification(2) and coating(3) are considered to have reached a satisfactory level. Deactivation(4) is still in a state of flux. Quantitation(5) is the least satisfactory aspect of capillary GC. Scope expansion(6) will be helped by the introduction of new phases of high thermal stability and by the adoption of solutions exclusively applicable to capillary GC. Evaluation of (glass) capillary GC columns is a rapidly developing field. Hopefully the number and complexity of test or polarity mixtures will not expand much further and it will be possible to make a clear and generally acceptable choice. The preparation and evaluation of ever-improving capillary columns is important to an ever-widening group of chromatographers. Our opinion on selected topics in this already vast field is summarized in the following overview.     

Faster GC analyses performed by flow programming in short capillary columns

The technique of programming the carrier gas flow rate in gas chromatography, especially in connection with the use of capillary columns shorter than 10 m can significantly accelerate GC analyses. Equations for calculation of the parameters of the exponential flow function and retention data are described. The effects of flow programming in a short capillary column are shown in a few chromatograms. Different programming rates are tested and compared with temperature programming.     

Development and evaluation of wall coated open-tubular columns for GC analysis of individual polychlorinated biphenyl isomers

The present article describes the development and testing of capillary columns for analysis of individual isomers of polychlorinated and polybrominated biphenyls, pesticides, and other halogenated hydrocarbons of environmental and biological importance.     

Computer-controlled vacuum backflush for capillary GC

A vacuum-pump-operated backflush system has been developed for applications involving high-speed, repetitive GC analysis of gas streams containing ppm and ppb levels of organic vapor. The system uses an injector capable of cryofocusing and a relatively short length of 0.25-mm i.d. fused silica column for the separation of relatively simple mixtures of volatile compounds. Analysis times typically are in the 5–10 s range, and backflush times are in the 2–5 s range. Gases from the flame ionization detector are used as the backflush carrier gas, and no modification of the detector is necessary. A procedure is described which allows the average gas velocity to be measured during backflush operation. The minimum backflush time is directly proportional to the analysis time and to the square of the column length, making this system most useful with short columns and short analysis times.