Chromatography Forum

I am working a GC-TCD in which I have two packed columns. One is poropak Q and one contains molecular sieve 5A. The gases that I want to identify are xylene/benzene/toluene, CO2, CO, O2. My carrier gas is Helium. I have a six way valve that takes care of sampling and injection.
I first saturate my helium gas with o-xylene by bubbling it through liquid xylene placed in a water bath. Then i inject the sample to verify the amount of xylene in my GC. The problem now is that I cannot seem to detect any peaks at all... I am suspecting that there might be better packing material (rather than poropak q) that can help me identify my xylene peak.. Is my hypothesis valid?

Please advise.

Another thing... is there a rule about the size, length, material of packed columns that we have to use?

Did you burn out the filament in your hot wire TCD?

Perhaps your valve is not injecting?

To separate such a wide range of analytes you really need two different types of columns or subambient oven conditions with programming to temperatures above 100°C.

Many columns will separate BZ/Tol/Xy with separation of the fixed gases as a separate earlier eluting peak.

To separate O2 and CO2 you need a Mole Sieve (5A or 13X) or a Carbon Sieve (G or Carboxen 1000).

These don't separate the aromatics in a timely manner.

No peaks means no flow, no sample injected, or your detector is broken.

Good luck in finding the fault.

best wishes,

Rod, the short timer (two more days)

Thanks for the reply, Short timer Rod.

I am sorry to confuse you. My TCD can detect peaks except for the xylene. It can detect O2 and N2, which by the way is also my concern, i am suspecting there is a leak somewhere because I can still detect air even after hours of purging with He.

maybe I'll try to clean my column poropak q...

If for example I am to replace the packed column, how much packing materials and how long would the packed column be?

Help!

I noticed that you are saturating the carrier gas with xylene, then you don't see a response for xylene. If the carrier is truly saturated with xylene, the xylene signal should be constant, and you would not see a xylene signal when you injected more xylene.