Chromatography Forum

Mot sure if this should go under CG. GCMS or Data systems... but I figure users of MS Chemsation are most likely to see it here...

To get good separation (for MS library searching) I need to cool the GC oven sub ambient... but I did not want to deal with the hassle and size of LN2 dewars , so I had the CO2 option installed... but I go through a tank in less than a day!

In the method I set cryo cooling to only be used when the temp is at or below 35C... If I understand what that setting means...

Program:
10C hold 5min
Ramp to 35C at 3C/min
Then Ramp to 300C at several rates

Quick cool is NOT Checked

That means it is only using CO2 cooling for the oven for about 14 minutes during the run, and I THOUGHT when the oven was cooling down ONLY AFTER the oven got to 35C... Which would keep the CO2 from running out too quickly...

But I paid attention when the run ended , and as soon as the the oven started cooling back down from 300C. the CO2 turned on full force! No wonder it emptied so quickly!!!!

So it does not seem to doing what I think I set t to do...

Is there some way I can prevent that? Do I have a software setting issue, or a hardware issue?

Any help would be appreciated... Cooling REALLY helps the separation!

Thanks,
- Karen

Hello

1.If you want use coolant only for oven temperature programming not for cooling oven after run, you need to have "Quick Cryo cool" option OFF. So in this case you will use coolant only to achieve temp lower than ambient.

2.To minimize coolant consumption connection between CO2 and valve in GC oven should be as short as possible - cylinder should be very close to GC or else tubing with CO2 should have really thick insulation. Otherwise even if you're using CO2 for short time in GC run the consumption will be high.

3. If you think "Quick cryo cool" is working all the time (even if it is off) I'd suggest create method from scratch - load method: GC_def.M and create new method based on deafult method. If it still (Quick cryo) working in on/off position perhaps there is bug in Chemstation or it is GC firmware issue.

Regards

Tomasz Kubowicz

You could also program the settings into the GC itself with the Chemstation disconnected and see if it works correctly, that will tell you if it is hardware related or software related. Setup and program the cryo from the front panel of the GC, then use the Start button to start the cycle and see if it still blasts CO2 at the end of the run.

Those small tanks though don't hold very much. I used to have a cryo unit on a Tekmar 2000 purge and trap and even the little it used to cool the trap would burn through a tank in just a few days. But it is much easier to handle those CO2 bottles than it is the Nitrogen Dewars we used to use on the old 5995 GCMS we had.