Ethylene detection in Air

[mruffo]

Hello -

I am new to the gc world.

I am using a Varian CP-3800 gc. I have a CP-PorabondQ column, 25m x 0.32mm ID. Helium carrier gas. FID.

I have two standards, ethylene in air @ 3ppm and 10 ppm (of ethylene).

I have been trying to develope my method, and continuously get one peak, which, when running zero air, appears as well - so I think I am not picking up ethylene in the chromatogram.

I have varied colum temperatures from 35C up to 200C with no drastic change in results.

Can anyone offer any pointers or ideas at what I should look for?

I have run the machine with a GC-GASPRO column, which gave very nice peaks for air and ethylene. I was told by Varian that the CP-PorabondQ would give even better results, but not so far.

Thank you!

[chromatographer1]

There are good reasons for the results you are seeing.

The porous polymer phase is quite small and is sample capacity limited as far as focusing the injection sample analytes.

The GasPro phase column tends to focus the sample components you have to a better degree than the porous polymer phase and does not retain a background amount lost in the pores of the porous polymer phase column.

The sample peaks are probably broadened out on the porous polymer column until you saturate the porous polymer phase with the analytes you wish to measure. This is not unusual behavior.

A thick film methyl silicone column will also give you excellent results at low levels like the GasPro column. A properly deactivated alumina column should also work well.

best wishes,

Rod

[mruffo]

Rod - thank you for your input.

I am guessing then that I would be better off working with the GS-GASPRO column, or will the PorabondQ column improve in peformance once I saturate the porous polymer phase? Or, is the Porabond column just really not the right column all together?

Thank you.

[chromatographer1]

If it were my choice, I would use the GasPro or use a micropacked porous polymer column.

best wishes,

Rod