Separate problems

[Cilyen]

Hi everyone,

I would like to separate NH3, propane, hexane and it's isomers. Which column would be suitable for this task?
Thanks for your help in advance!

[chromatographer1]

A porous polymer column is one choice.

A thick film capillary or heavy loaded methyl silicone phase packed column would be the best choices.

best wishes,

Rod

[Cilyen]

Thanks a lot for the good idea!
We took a Rt-U-BOND type column into the GC. It can separate the NH3, propane and hexane.
Our further problem is that there are other products from the reaction: propylamine, dipropylamine and tripropylamine, and the tripropylamine and dipropylamine takes a very long time to eluate. They have huge tailing peaks.
We used TCD to detect the NH3 and FID for the further componets. The TCD parameters were the following: carrier gas was H2, TCD temperature:250°C, and the current was 50 mA.
We found, that the TCD detector sensitivity was very low and it was decreasing continuously. I made a regenaration run for the TCD, increased the TCD temeprature to 350 °C and set the filament current to 0 mA. I kept the detector at these parameters for 1-2 hours to get better sensitiyity. But it didn't help. Now I don't see any peaks on the TCD chromatogram.
What do you think what is the problem? Thank you for your help in advance!
Best regards,
Cilyen

[Johnny Rod]

TCD current gives it the sensitivity. Increse it to 20mA and the peaks will be larger. For this you may need a lower TCD temperature and higher filament temperature (depends which parameters your software controls).

[AICMM]

Cilyen,

Regarding U-bond, what kind of peak shape did you get for the ammonia and what kind of separation from the propane?

Regarding the TCD, consider a hot filament and ammonia may not be the best combination. Also consider that the TCD is concentration dependent so the lower the flow the more the sensitivity. Also consider that TCD sensitivity depends on temp gradient between filament and body so lowering the temp to 200 or even 180 might improve sensitivity. Since you are using two detectors, you might consider parallel channels, one for ammonia (preferably with backflush), one for hydrocarbons and heavier amines.

Rod,

Do you think a methyl silicone will hold ammonia enough to get it away from propane (or, really, the other way around, hold up the propane enough to get the ammonia in front?)

Best regards,

AICMM

[chromatographer1]

If the phase has been made non-polar enough (the silinols eliminated) and the surface also neutralized enough, it may be.

Of course, how long that can remain if water and ammonia are present is anyone's guess and may be temperature dependent.

It is worth a shot. The Hayes C copolymer or the Chromosorb 103 are the first choices to try.

A combination column (which everyone but the experienced process analyzer chemist wishes to avoid) would also be worthy of a trial. Of course, I would combine a short thick film methyl silicone with a tuned length of base deactivated PEG column.

Rod