Chromatography Forum

Can someone help me understand where in the GC system gas flow restrictors are used and for what reason...i.e., safety concerns or equipment regulation? your help would be greatly appreciated!

That's a broad question. I can tell you where I use a fixed restrictor.

I have systems that employ the Agilent "Dean's Switch" so that I can perform heartcuts from one phase (5-phase) to another (Wax). To make this work, you have to use a fixed restrictor (nonpolar, fused silica) so that the switch sees close to equal flows from the second column (going into a mass spec.) and the first column (into a flame). On one of my systems, for instance, I have a 30 m x 0.32 mm x 0.5 µm wax as the second column (4.32 psig feeds that column at the switch). The fixed restrictor from the switch to the flame is 2.0 m x 0.20 mm. The system is balanced with a 9.54 psig head pressure on the first column (30 m x 0.32 mm x 0.5 µm).

I can make nice, clean cuts with this setup and the peak shapes are pretty good on both the first and second columns. I have a thermal desorption system feeding the first column on this system.

Actually Agilent gas regulators are the PRESSURE regulators (and feedback is on the pressure channel). To measure such a low flows - you need the small catharometer. IMO they just not have one, they control and measure only pressure.
Desired flow is achieved installing proper restrictor (btw GC capillary column is also restrictor). Setting gas channel to flow - just instructs GC adjust pressure to keep flow constant. Try to trick the GC specifying wrong column parameters - and compare actual flow displaying on GC and masured with independent flow-meter.

Instrument keeps the pressure - you get the calculated flow through the hole of specified diameter (as far i remember restrictors are color-coded)

Additionally, if running hydrogen for fuel or carrier; there is tyically a snubber just after the regulator (at the tank) to keep a line break from causing a large hydrogen leak.

Our 5890 systems had a changeable frit in the flow controller.