Chromatography Forum

We are analyzing Nitrogen gas By Agilent GC 7890A with Chemstation software.
We have fixed Gas sampling valve to the instrument, but it is very difficult to control the sampling volume as we are unable to maintain constant flow for every injection during analysis.
Is there any provision / additional attachment so as to control sampling gases flow to 1.0 ml / min.
Thanks and Regards,
Sitaram

This depends a bit on what your are sampling - but the first thoguth that comes to my mind is if you can feed a pressure regulated stream through a flow restricter to an exit with fixed pressure on the other side, you shold have constant flow.

Thus, one possibiltiy would be to put a regulator on the output from the gas stream followed by a needle valve, the gas sampling loop and an exit to atmosphere. This would work only if there could be a 20 pound pressure drop through the regulator.

It is not considered good practice to have flow through the gas sampling loop when you make an injection for reasons that you have already found. Fill the loop, stop the flow and wait for about 15 seconds for the pressure in the loop to come down to atmospheric, and then start the run. This will give you reproducible results.

Gasman