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GC Valves

http://www.chromforum.org/viewtopic.php?t=49854

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GC Valves

Posted: Thu Sep 28, 2017 1:43 am
by MLT
Hi! I am a first year MS student and I badly need help.

I am trying to analyze a mixture of gases including H2, CO2, CH4, CO, and H2O using a GC 7890A TCD. I read that it is possible to use parallel columns and switch between these columns to analyze H2, CH4, and CO in the first column (Molsieve 5A), then CO2 on the second (I'm planning to use CarboPLOT on this one, but I am also unsure if it could work with moisture?). However, I am unaware on how to install the columns and if my GC has the required valves installed. The GC in my lab has been here for about 5 years now but no one seems to have used it fully.

Is there any way for me to confirm if our GC has these valves, and if it is possible to install 2 columns on our GC?

(Sorry if my question sounds stupid, just completely clueless here :cry: )

Re: GC Valves

Posted: Thu Sep 28, 2017 2:45 pm
by GasMan
If you can give me the serial number of your GC I can see what the GC was initially shipped with.

Gasman

Re: GC Valves

Posted: Mon Oct 09, 2017 1:56 am
by MLT
If you can give me the serial number of your GC I can see what the GC was initially shipped with.

Gasman
Our GC's SN is 153200229120004.
Thank you so much!

Re: GC Valves

Posted: Mon Oct 09, 2017 1:15 pm
by GasMan
MLT,

The number that you have given me is not an Agilent serial number. You will find the serial number on the front of the GC below the keyboard. It should start with the letters 'US' or 'CN' followed by 8 digits.

Gasman

Re: GC Valves

Posted: Tue Oct 10, 2017 8:03 am
by MLT
MLT,

The number that you have given me is not an Agilent serial number. You will find the serial number on the front of the GC below the keyboard. It should start with the letters 'US' or 'CN' followed by 8 digits.

Gasman
Oh sorry, it should be CN12441113. Thank you very much!

Re: GC Valves

Posted: Thu Oct 12, 2017 1:12 pm
by GasMan
MLT,

This GC was originally shipped with a packed and a capillary inlet, a FID and a TCD and two valves. The valves are two six port gas sampling valves, one connected to the packed inlet and the other connected to the capillary inlet.

What is the expected concentration of the methane in your sample? If this is above 10 ppm, then all of the gases in your sample can be detected on the TCD. The FID will only detect methane, as this is the only gas that will burn in the FID flame and give a signal, but it is more sensitive to methane than the TCD and you can detect ppm levels.

The Molesieve 5A is OK for most of the compounds except for water and CO2, which are adsorbed, but molesieve 5A is about the only column that will separate H2,CO and CH4. You really need to have a two column system where the columns are in series. This would require modification of the GC, where one of the gas sampling valves is changed to a column isolation valve. I suggest that you contact Agilent or Yougin Scientific in your country who should be able to advise you on what changes are needed.

Gasman

Re: GC Valves

Posted: Fri Oct 13, 2017 10:34 am
by MLT
MLT,

This GC was originally shipped with a packed and a capillary inlet, a FID and a TCD and two valves. The valves are two six port gas sampling valves, one connected to the packed inlet and the other connected to the capillary inlet.

What is the expected concentration of the methane in your sample? If this is above 10 ppm, then all of the gases in your sample can be detected on the TCD. The FID will only detect methane, as this is the only gas that will burn in the FID flame and give a signal, but it is more sensitive to methane than the TCD and you can detect ppm levels.

The Molesieve 5A is OK for most of the compounds except for water and CO2, which are adsorbed, but molesieve 5A is about the only column that will separate H2, CO and CH4. You really need to have a two column system where the columns are in series. This would require modification of the GC, where one of the gas sampling valves is changed to a column isolation valve. I suggest that you contact Agilent or Yougin Scientific in your country who should be able to advise you on what changes are needed.

Gasman
Thank you very much for this!

The methane would probably of low concentration but I will probably just use TCD for this. Is it better to just buy a column that would detect all these gases? I read from another topic that I could use a Mol Sieve 13X for this or a ShinCarbon column?

Again, thank you so much for your help!
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