Chromatography Forum

Hello, everybody!

I would need some help with our new CarboPlot P7 column for analyzing a mixture of gases (CO, CO2, CH4 etc.) using He as carrier and a VICI gas-sampling valve. We obtained no peaks with the method recommended by the producer (30°C for injector, 30°C for column, 80°C for TCD and a pressure of 11.7 kPa). We tried increasing the temperature; however we did not increase the pressure too much, since the producer recommended that we should avoid that. Still no results!

Can anybody help me with this problem?
Elena

gcmbsi,

Without knowing the dimensions of your column, the only comment I can make is that your pressure sounds really, really low. That could explain the absence of peaks. Either they are taking a really long time to come off the column and/or they are so smeared out that you cannot discern them from the background.

Best regards.

If that is a 25m 0.53mm ID column so 2 psi (11.7kPa) sounds reasonable with a 10-25? µL sized sample loop.

A00494-A00496 application notes from Varian show low pressures at 30°C.

If you are injecting a large loop you will overload the column and smear the peaks, especially if you are looking at very small levels in certain matrices.

I think it likely that you have a detector with too much dead volume to handle the amount of sample injected

OR

You have TCD detector set up with the wrong reference flows. (or the hot wire is burned out ! )

Of course, it may be a leak.

Without knowing more details, that is all I can suggest at this point.

best wishes,

Rodney George
consultant