Tapered restrictor

Figure 6.13 Flow restrictors of different design A, linear B, tapered C, integral and D, frit. On the right side is shown a modified high pressure cell for UV detection using open tubular columns.

The cyclone separator consists, in part, of a large-diameter cylinder with its central axis mounted vertically. A restrictor or BPR introduces the sample into the cylinder through a tube, pointed slightly down from horizontal, parallel to and nearly touching the inner wall. The cylinder acts as an expansion chamber. Its large volume allows the velocity of the expanded fluids to slow down. Heavier, nonvolatile components hit the wall, coalesce, and run down to the bottom, which is often tapered to a smaller diameter. A gas exit tube, often on the axis of the cylinder, allows the gas phase to escape out the top of the device. The density of the gas may still be 0.05-0.1 g/ cm. This fluid is sometimes recompressed and reused if it is pure enough. 

The end of this tube was tapered, sized, and cut to form a restrictor, R, in the manner previously described (23). The tapered end narrows to an aperture of approximately 3-5 urn diameter over a length of 2 to 4 cm. This restrictor is housed inside a 50 cm length... 

One instrument configuration utilized in this laboratory is shown in Figure 5. In this instrument the column was mounted in a constant temperature gas chromatograph oven, which also served to heat the air circulated through the DFI probe. A zero dead volume union is typically used to connect the column to a short length of 4-8 ym i.d. or contoured (tapered) fused silica restrictor. The restrictor and probe tip are heated to compensate for cooling due to decompression of the fluid during the DFI process. 

Lord, G.A., et al.. Tapers and restrictors for capillary electrochromatography and capillary electrochromatography-mass spectrometry, J. Chromatogr. A, 768, 9, 1997. 

In the SFE DI experiment the restrictor was inserted into an SFE sample collection tube, which was kept cold by immersion into dry ice. These experiments were also repeated five times, each time with a fresh sample, and the volatiles were trapped/combined in the same tube. After the SFE isolations, about 1 mL of methylene chloride was added to dissolve the residue sticking on the side walls of the sample collection tube. The extract was then transferred into a small tapered vial. The vial was kept under dry ice and concentrated with a gentle stream of nitrogen to 0.5 mL, and 1 pL of this extract was manually injected with the GC in splitless injection mode. For experiments 2 and 3 an SFE chamber pressure of 4000 psi was used. These two experiments were also performed on a different gas chromatography mass spectrometry (GCMS) system, the Hewlett Packard (Palo Alto, CA, U.S.A.) 5890 Series II GC coupled with a 5970 mass selective detector. 

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