Chromatography Forum

Hello,
I am trying to separate water, isobutanol, and acetic acid on GC (with TCD detector) and equipped with a porapak T column. (Column temperature is 170, TCD 200°C and INJ 200°C) But isobutanol and acetic acid peaks are too broad to being resolved properly. How can I fix the broad peaks? I'd be grateful if anyone can help me!:)

Assuming you want to keep using the same "T" column other than increasing the flow rate of your carrier there is little you can do.

Do you have any other columns?

best wishes,

Rod

May be porapak Q column I can use.. but I have only T column, now. Would you advise to use porapak Q column? thanks Rod

No, I would believe that other columns would be preferable. Too bad you can't get other columns.

You could try lowering the temperature and using different oven temperature ramps and see if that improves your chromatography.

best wishes,

Rod

Dear Rod ,
I would like to ask one more question. If I could get a different, suitable column for this separation which column would it be? Thank you very much for your help Rod

Best wishes

I would try a column in glass or fused silica lined SS packed with 11812-U, 5% Carbowax 20M on Carbopack B from Supelco or optionally order a custom column with 1% SP-1000 on Carbopack B.

I believe the order of elution will be water, isobutanol, acetic acid.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com

Thanks for all your help Rod. I will try to do your suggestions
best wishes

Dear Rod
I tried everything but, unfortunately I did not succeded with Porapak T column. I am planning to get the columns you have suggested. But I wonder whether the columns can tolerate 20% and maybe much more higher water percantages or not.
Do you think these columns can resist against water? Thanks a lot in advance

The prime consideration is the temperature you will have the column maintain. If you keep the temperature low enough that water is retained in liquid form on the column almost any column with a phase coating will be damaged in time.

But if you drive off the water during the process of your analysis and try to keep the water in vapor form the columns I suggested will last a reasonable time.

It should not take an excessive temperature to achieve your analysis and to remove water. I would guess just elevating your column temperature to a temperature of 90-120°C for a few minutes should be adequate. I would start at a lower temperature initially.

I would use a higher level of Carbowax 20M phase coating over a smaller amount, although the separation of water from the alcohol and acid will be larger with a lower coating, the separation of the alcohol and the acid will be less as the phase percentage decreases. A balance of the proper amount of phase is needed. I suspect a level closer to 5% will give you the results you seek.

best wishes,

Rod