Shin Carbon and Mol Sieve 5A in series for permanent gases

Discussions about GC and other "gas phase" separation techniques.

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I have a rather different system where I try to separate and quantify O2, N2, CH4, CO and CO2. The carrier gas is Helium. I have ShinCarbon and Mol Sieve 5A in series in the beginning. After O2 and N2 are eluted I shortly switch the valve where MolSieve is bypassed and only ShinCarbon is at play. After CO2 is eluted I switch back to the configuration where MolSieve is in the picture again. At least this is the ideal case.

My parameters:
Flow control with a flow rate of 10mL/min
Injector temp: 100 C
Detector: HID at 280 C.
Injection type: Split with a split ratio of 2
Carrier gas: He
Switching times: From 0 to 9 min the two columns are in series. Between 9 and 13 min it's only ShinCarbon and then it is switched back to the position where the columns are in series.

My problem is I cannot seem to arrange the switching time in an optimum manner. Either CO2 is eluted to MolSieve (which is not ideal) or part of N2 is eluted to MolSieve as well (not ideal but I can survive).

My question: Is there any parameter I can optimize to retain CO2 on ShinCarbon a bit longer so that it doesn't go through MolSieve.

I hope it's not confusing. Thank you very much in advance for the help!
O2, N2, and CO come off the Shincarbon pretty quickly so you should be able to switch the valve much earlier than 9 minutes. Lets the C1 and CO2 off the Shincarbon and then back to the sieve.

Make a run with just the Shincarbon in line to establish the cut times (unless this is a single valve configuration....)

Best regards,


thanks a lot for your reply. I have been trying to switch much earlier as you suggested. However, even if I switch right after the O2 and N2 come off of the ShinCarbon (around 2 min) or a bit later (around 3min) when I switch back to MolSieve there are two peaks (although small) appearing resembling O2 and N2. It seems like a bit still goes to MolSieve. I guess I will have to live with two different injection when I need to separate O2, N2 and CO2 at once.

I will still work on it and update in case I get an optimum result.

thanks again and best regards.
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