Chromatography Forum

Hi,

I would like to condition 5 columns which are in the same GC (Agilent 6890N) oven, they have the following characteristics:

Col. 1, Col. 2, Col. 5 -> Haysep Q, 3/16" o.d., max. temp. 275ºC (new packed columns)
Col. 3 -> Porapack Q, 1/8" o.d., max. temp. 250ºC (max. temp. assumed according to internet information) (used column that has been stored for some time without end caps or plugs)
Col. 4 -> Molsieve 5A, 1/8" o.d., max. temp. 400ºC (used column that has been stored for some time without end caps or plugs)

According to the information included in the User Manual, I would like to do the following:

Condition the five columns at the same time at a temperature of 250ºC - 30ºC = 220ºC according to the following temperature ramp:

Init temp = 50
Init time = 5
Rate 1 = 15
Final temp = 220
Final time 1 = 720

And establish the following flows:
Col. 1, Col. 2, Col. 5 -> 50 mL/min
Col. 3, Col. 4 -> 25 mL/min

I think that the end of the columns that are normally connected to the detectors (microECD and FID) should be placed out of the oven and I that I should cap the detector fittings. Am I right?

Do you think that the temperature is correct for this type of columns? Time should be longer than 720 min? What do you think about flow rates?

I am doing this because I cannot see any peak with the FID (and methanizer) when trying to detect CH4, CO2 and CO.

I thank you in advance for your help.

Flows are no problem although I would use max flow for sieve and 20cc/min for the polymer packings.

temperature ramp is a poor choice. I would have slowest possible ramp with holds at intermediate temperatures 150C and 180C for an hour each. I would use a final hold at 200C for 18 hours.

I would not put ends of column outside of oven! BAD BAD leave column ends in oven and cap the detectors as you indicated.

I would not condition packings above 200C unless you intend to use them above that temperature. The higher temp you use for the polymer packings the more damage you will inflict on them. If water is present in MS packing you WILL DAMAGE the packing above 200C. It will take days of conditioning to remove all-most of the water. Longer conditioning times at lower temperatures will cause less damage to the MS packing. There is no advantage in using higher temperatures for the MS except quicker conditioning, and that comes with a cost of increased damage and poorer chromatography. Proceed at your own risk.

best wishes,

Rod

Thank you for your quick answer. I will consider all your comments!

.. Is it better to let column ends in the oven, then?

Thanks again.

Of course, it is.

Why deposit 'junk' at the end of the column? Why in the world should the column ends be kept cool?

You will ruin the MS column if you do that, unless you like tailing peaks in your chromatography, especially the CO peak. I like symmetrical peaks, myself. But you may differ.

best wishes,

Rod

What carrier gas are you using with your methanizer? What temperature are you heating the methanizer?

Can you remove it and place it in another oven with air carrier flow through it?

Have you considered just replacing the packing in your methanizer?

Why do you store columns without capping the ends?

Rod

I'm using Ar/CH4 as carrier in the microECD section and N2 in the FID. I flush the gas with hydrogen through the nickel powder filled methanizer.

The methanizer is at 385ºC.

So do you recommend me to flow air through the methanizer? I had read that oxygen can degrade the methanizer by oxidizing the nickel catalyst powder, why should I flow air through it?

I'm quite new with this type of analysis, so sorry if I ask obvious questions...

I didn't meant to let the end of the column itself out of the oven, but a tube connected to this end (the one that I disconnect from the detectors). I was afraid about the Ar/CH4 mixture getting into the oven at this high temperature... According to the manual I had impression that I should disconnect the columns from the detectors, you think I shouldn't, am I right?

From now on I will store columns capping the ends, no doubt.

Thank you for your help!

I would condition all the columns with nitrogen. They could be attached in series with the MS first followed by the porous polymer columns. Or condition them individually.

I would not allow any carrier containing methane to elute into the hot oven.

A Methanizer can 'carbon up' and they must be oxidized to remove these deposits before reconditioning with hydrogen. All this is questionable due to the low (<600C) temperature most lab ovens can reach. It is more practical to repack the methanizer with new catalyst. This catalyst is available from Agilent and Gow-Mac I believe. Avoid creating voids when you repack.

FYI The 'pigtails' attached to the column ends are NOT the column ends.

It is still better to keep them inside the oven. Please cap off the detectors.

Your catalyst temperature is fine.

Good luck and best wishes,

Rod

Sorry to keep bugging you, Rod,

when you say 'Please cap off the detectors' you mean that the detectors fittings should be 'closed' with a no-hole ferrule and column nut, for example?

I saw in this page:
http://www.chem.agilent.com/Library/Sup ... A20343.pdf

that they use the word 'cap off' as 'plug' and I'm a little bit confused...

Thank you very much for your attention.

A Cap means a device which covers and seals the fitting containing a hole.

A Plug means a device which goes inside a hole in a fitting and seals it shut.

You can cap an oil well and you can plug an oil well. Both stop the flow of oil in or out of the well.

You say po - tah - toe, I say po - tay - toe, but both are potatoes, ie french fries.

I hope I have not confused you.

best wishes,

Rod