Hi David,
Under the advice of Paul Eby of Alberta Innovates, I was able to trap CH4 using a short loop (18" or so) of a GS-Q 0.53mm ID GC column in place of the nickel wire on a gas bench cryotrap. I had a chemical and slush CO2 trap in place first because I was not interested in the CO2, but I think you could easily use one of the cryotraps that you mention.
On my setup, I have two traps on the same pneumatic piston at 90 degrees to each other and going to two separate cold traps. So I get three traps for the price of two and software control. But I backflush my CO2 out of trap one as soon as it is raised. If you could slow down the CO2 enough after raising the trap, you might be able to get away with just two pistons and full automation.
Cheers, Ben
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Wolfram Meier-Augenstein (aps)
Sent: Thursday, May 26, 2016 8:19 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Using Precon for CH4 and CO2 separation
Hi David,
How fast will your sample gas flow through the cryo trap?
CH4 is notoriously difficult to trap, even with liquid N2 it has to be slowed down e.g. by filling the trap with zeolites or similar. So, depending on your set-up you could easily use liquid N2 to trap CO2 while still letting through CH4.
What you need to watch is that trapping CO2 at whatever temperature will also trap any traces of humidity present in the gas phase above your cultures.
Depending on the diameter of your trap and amount of moisture, frozen water accumulating at the top of the trap (about level with the cryo liquid) might block your trap.
Best,
Wolfram
Sent from my BlackBerry 10 smartphone.
Original Message
From: Denhaan, David
Sent: Thursday, 26 May 2016 16:08
To: [log in to unmask]
Reply To: Stable Isotope Geochemistry
Subject: Re: [ISOGEOCHEM] Using Precon for CH4 and CO2 separation
Wolfram,
Thanks for the reply. I was going to use liquid nitrogen for the CO2 trapping. Is that too cold? Is calculating the trapping capacity of the liquid nitrogen trap as easy as calculating the volume of tube and using PV=nRT and perhaps cutting it by 50% since I don't want to block the flow? And you're comfortable that trapping of CO2 is thorough enough not to affect the CH4 analysis?
Thanks,
David
David DenHaan
Laboratory Technician
National Laboratory for Agriculture and the Environment Ames, IA
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Wolfram Meier-Augenstein (aps)
Sent: Thursday, May 26, 2016 9:39 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Using Precon for CH4 and CO2 separation
Hi David,
What you propose doing should work. You could use a methanol/liquid N2 mix (-98C) to be sure to trap CO2 without it breaking through if you feel dry ice/acetone (-78C) might be cutting it too finely.
Best,
Wolfram
________________________________
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Denhaan, David <[log in to unmask]>
Sent: 26 May 2016 15:20
To: [log in to unmask]
Subject: [ISOGEOCHEM] Using Precon for CH4 and CO2 separation
Dear List,
I'm trying to analyze CH4 and CO2 from the headspace of a bacterial culture with a labeled acetate substrate. Depending on the enrichment in CO2 and methane evolved I should be able to show which bacteria are active. I have a Precon hooked up to the gasbench GC and a Delta V. I 'm hoping to trap the CO2 from the headspace on the manual trap this would let the CH4 pass through to be combusted and measured. When that's done I would raise the manual trap and measure the CO2. Is this a sound approach? I'm worried about how much CO2 can be trapped on the manual trap and how complete the trapping is. If CO2 comes through the manual trap I won't be able to distinguish it from the CH4.
Thanks,
David
David DenHaan
Laboratory Technician
National Laboratory for Agriculture and the Environment Ames, IA
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