Tubing fused-silica columns

Automated gel permeation chromatograph (Cleanup XL, Abimed Gilson) equipped with 5-mL loop and chromatographic tube, 25-mm i.d., 600-mm long, filled with 52-g of Bio-Beads, S-X3, 200 00 mesh, 33-cm gel bed length GC Gas chromatograph equipped with a split/splitless injector, autosampler, DB-1 fused-silica column, 30 mx 0.25-mm i.d., 0.25-p.m film thickness and electron capture detector... 

Diastereomer ratios were determined by gas chromatography. Since the aldol adduct undergoes retroaldol reaction on the column, it must be silylated prior to injection. Approximately 5 mg of the crude adduct is filtered through a short plug of silica gel to remove any trace metals. The material is taken up into 1-2 mL of dichloromethane in a 2-raL flask or small test tube. To this solution are added 4-5 drops of N,N-diethyl-1,1,1-trimethylsilylamine and a small crystal of 4-(N,N-dimethylamino)pyridine (Note 11), The solution is stirred for 2 hr and injected directly onto the column. (Column conditions 30 m x 0.32 mm fused silica column coated with OB 5, 14 psi hydrogen carrier gas, oven temperature 235°C). 

Figure 2. Schematic diagram of column tip, second version. 1, Fused-silica column I.D. 0.22 mm 2, chromatographic bed 3, glass fiber filter frit 4, drawn-out 50 ym fused-silica tube 5, high temperature epoxy coating...

Pyrolysis. In the pyrolysis experiment, typically 30 mg of sample was heated in a quartz tube at 400°C for 24 hrs at 2xl0"6 torr. Tars were trapped at room temperature and the more volatile products at liquid nitrogen temperature. These two fractions were analyzed by GCMPES (MPD-850) using a 25m x 0.25 mm i.d. OV-101 fused silica column and by GCMS (Kratos MS-25) using a 30m x 0.25 mm i.d. DB-5 column. 

For a period of time, OT columns that had characteristics intermediate between those of WCOT and packed columns were popular. There were two types, but they were similar. Support coated open tubular (SCOT) columns had a thin layer of solid support coated on the inside wall of a capillary tube of larger diameter than that used for WCOT columns. This layer was coated with stationary liquid similar to packed columns. Porous layer open tubular (PLOT) columns were similar but made differently for example, the solid support was added while the capillary tube was being drawn. With a few exceptions, SCOT and PLOT columns are no longer popular because wide diameter WCOT fused silica columns are as good, more stable (no layer to flake off), and easier to use. Subsequent discussion will be restricted to WCOT columns. 

Fast peaks were generated using a modified fast sampling valve (Linear Dynamics, E. Pepperell, Ma.), to Inject butane (Matheson, Instrument grade) onto an uncoated 0.060mm x 2.0m fused silica column. The 1070 Injector cap was drilled out to allow a piece of 1/16 steel tubing to seal the fast sampling valve with the 1070 injector body. The standard gas inlet line... 

The authors have recently employed fused-silica tubing ais a column material aind found that micro packed fused-silica columns possess high efficiencies(3-7), owing to the smooth auid inert surface of fused-silica tubing. In previous work(4-6), 20-50 cm columns were connected in series in order to attain laurger theoretical plate ntmbers. Theoretical plates auround or in excess of 100,000 could be produced on 1.5-4 m micro packed fused-silica columns in the reversed-phatse ( ) and size-exclusion chrcmiato-graphy(4,6). 

Figure 1.2 Various columns and materials employed for capillary gas chromatography (a) left 25 m x in. o.d. stainless steel capillary column in a pancake format, center 30 m X 0.25 mm i.d. aluminum-clad fused-silica column, right blank or uncoated stainless steel capillary tubing o.d. (b) 60 m x 0.75 mm i.d. borosilicate glass capillary column for EPA method 502.2 (c) 30 m x 0.25 mm i.d. fused-silica capillary column also pictured is a typical cage used to confine and mount a fused-silica column.

Three steps are involved in the preparation of a fused-silica column (1) the high-temperature extrusion of the blank capillary tubing from a preform, where the capillary receives a protective outer coating in the same process (2) the deactivation of the inner surface of the column and (3) the uniform deposition of a stationary phase of a desired film thickness on the deactivated inner surface. In this section the extrusion of fused silica is described the procedures employed for the deactivation and coating of fused-silica capillaries are presented in the following section. 

Capillary Tubes Figure 12.42 shows a cross section of a typical capillary tube. Most capillary tubes are made from fused silica coated with a 20-35-)J,m layer of poly-imide to give it mechanical strength. The inner diameter is typically 25-75 )J,m, which is smaller than that for a capillary GC column, with an outer diameter of 200-375 )J,m. 

Capillary columns are fabricated from thin-walled stainless steel, glass, or high-purity fused silica tubing (the last is preferred for its inertness). Typical dimensions of the columns, which are coiled, are 25-200 m long and 0.2-0.5 mm i.d. 

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