Chromatography Forum

Hello,

I have a Perkin Elmer Autosystem XL with a 60/80 carboxen 1000 (15 ft) column and TCD detector. I currently have excellent results measuring CO, CO2 and CH4. Now, I need to measure methanol and I cannot detect it. I don't see the methanol exiting the column even when I let the program run for 40 minutes. The procedure I am using is the following: Carrier gas He (30 ml/min). 35°C (5 min) to 225°C at 20°C/min.
Is it expected that methanol would exit at very long times?
Do you think another column is more suitable for the separation? I have a 60/80 Porapak Q (6 ft), 100/120 Hayesep D (7 ft) and a MolSieve 5A (6 ft). Two of them in series could be a solution?

Any advice will be greatly appreciated.

Small molecules like methanol chromatograph well on Porapak Q, and you will separate CO, CO2 and methane, but any air gases (oxygen/argon/nitrogen) will coelute with the CO. You wan't get CO2 or methanol to elute of mol sieve, and though I'm not familiar with Haysep D I think the same would be true as retention is high.

Thank you for your advice.
I want to use N2 as internal standard. If CO and N2 cannot be separated with a Porapak Q, I should use the carboxen 1000.

CO and N2 are well separated using carboxen1000. The conditions of the experiment are: 30 ml/min of He carrier gas, 35°C during 5 min and then 20°C/min to 225°C. At these conditions N2 elutes at 6.2 min and CO at 7.9 min, which is excellent. Unfortunately, the methanol peak appears at 6.5 min which makes very difficult to separate it from the N2 peak. What would you recommend to further separate N2 and methanol peaks?.

Personally, I would change the temperature program. Methanol boils at 65C, so there's no reason to go to 225C. If you stay low temp for longer then you should stretch out that retention time.

thanks. I'll try that tomorrow.

You won't get methanol off of the carboxen. You'll need to switch columns.