High temperature gas chromatography: The development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases: Part 1

With the simultaneous development of blank aluminum clad flexible fused silica glass capillary tubing capable of withstanding temperatures up to 500°C, coincident with a series of special high temperature methyl polysiloxane polymers, it was possible to produce for the first time, long lived fused silica capillary columns containing thin films of thermostable stationary phases which could be maintained isothermally at 400425°C and temperature programmed to 425–440°C. The “bleed rate” here for a well conditioned column was 5 picoamperes or less. Under these circumstances, alkanes with carbon numbers in the C-90 to C-100 area were rapidly and efficiently eluted from these columns. By extrapolation here, one can easily detect certain compounds with boiling points in the 750°C range. Since this type of capillary column was found to possess certain favorable properties, it was thought that it will soon replace the packed column and will probably be more popular than the borosilicate capillary column for many high temperature applications. Moreover, evidence has now accumulated which leads us to further believe that the majority of analyses of “high molecular weight” compounds performed by Supercritical Fluid Chromatography (SFC), utilizing very narrow bore fused silica capillary columns at several hundred atmospheres, can be much more simply, much more rapidly, much more economically, and much more efficiently accomplished by gas chromatography utilizing this new generation of high temperature capillary columns.     

Hydrothermal treatment of fused silica capillary columns

The activity of fused silica capillary tubing has been shown to vary considerably, which severely influences the reproducibility of column deactivation and inertness. Methods for producing a reproducible, high activity surface with maximum hydroxylation by various hydrothermal treatments were evaluated. Columns pretreated with 20% nitric acid at 200°C for 10 hours, deactivated with D₄, coated with OV-73, and crosslinked with azo-tert-butane were found to possess excellent inertness for sensitive analytes such as alcohols, amines, and alkaloid drugs.     

Polysiloxane deactivated fused silica capillaries containing immobilized stationary phases

This article describes a method of preparing immobilized stationary phases which has arisen from the authors' work on polysiloxane deactivation of fused silica capillaries. Although acid treatment is often omitted with fused silica capillaries, there are good reasons for hydrothermal treatment of this column material. Use of Grob's peroxide method gave immobilized 0.25 μm films of SE-54; lowering of the immobilization temperature permitted immobilization of 0.1 μm films of the same phase.     

Gas chromatographic retention in uncoated fused silica capillaries

Understanding of retention in uncoated fused‐silica capillaries is of interest due to increased attention on precolumn backflushing in capillary GC. Uncoated capillaries offer several advantages as precolumns compared to coated precolumns. In order to examine the possibility of predicting elution temperatures of alkanes from uncoated capillaries a priori, several sizes of deactivated but uncoated fused‐silica capillaries were evaluated under various operating conditions. Retention was found to depend on dimensionless ramp rate (°C/t_M), sample loading (capacity), flow mode, and column dimensions (probably related to surface area).     

Strategies for compound identification and quantification using fused silica capillary column GC/MS

A test mixture containing 28 compounds plus their stable isotopically labeled analogs was analyzed on a daily basis for one month during a series of routine fused silica capillary column GC/MS analyses in order to establish the precision with which retention times and responses were produced. These long-term precision data were evaluated to determine how to best predict retention times and how to best reproduce quantification. Results clearly indicate that relative retention times should be calculated using the reference compound eluted most closely to the target compound and that quantification should be based on relative response using a chemically “similar” compound.     

Direct sample injection in supercritical fluid chromatography with packed fused silica column

A direct sample injection technique was developed for supercritical fluid chromatography in a packed capillary column, with carbon dioxide as mobile phase and a flame ionization detector. The method allowed solutions, neat liquids, and even solids to be introduced as samples. Also, extraction with supercritical carbon dioxide was combined with this method to separate polymer additives.     

Behaviour of fused silica capillaries subjected to gamma radiation. Part 2: Physical aspects

Five commercial varieties of uncoated fused silica capillary tubing used in high resolution gas chromatography were subjected to cobalt-60 gamma radiation. The advantages and superior performance of fused silica open tubular columns coated with OV-1 and subsequently immobilized or crosslinked in situ by radiation is reported in a previous paper in this Journal; however, in this investigation a loss in flexibility of irradiated capillaries was also noted. Quantitative measurements on flexibility were performed on specimens of irradiated fused silica capillaries, indicating that changes do indeed occur upon irradiation. Scanning electron micrographs also illustrate slight deterioration of the outer protective polyimide coating. Most surprisingly, it was also established that a variation does exist in the flexibility of the commercially available raw material studied.