Water vapour determination in hydrocarbon-air mixtures

[Robert Van Hale]

Dear Forum,
To make use of equipment on hand , and seeing that Porabond Q columns produce a focussed water peak , I would like to use GC-TCD to measure water vapour concentration in petrol-air mixtures.

Aside from the difficulties with handling water vapour , could this work using a capillary column? Air at 30 degrees C, 100% RH contains ~30 g/m3 water, so the range of interest is say 0.3 to 30 g/m3. I suppose the question is what quantity of water that can be determined by TCD ? Do I need to change to a packed column method and inject a larger sample perhaps ?

thanks very much for any hints

Robert

[chromatographer1]

There is no reason why it won't WORK, but the issue is how WELL?

If you can get the sample properly sampled and injected without discrimination onto the column your detection by TCD should be similar as that for methanol or propane.

On an industrial basis I know that a polar porous polymer might work better than a 'Q' polymer column. They also prefer to use micropacked columns with the 'R" polymer for peak symmetry and separation issues from volatile hydrocarbons.

Good luck in getting good standards which are critical to an accurate measurement.

Other detectors can be used with more sensitivity. See AIC or Valco or Gowmac.

best wishes,

Rod

[Robert Van Hale]

Thanks very much Rod,
that is some encouragement; useful notes too. For standards I can perhaps use the same technique as is used for calibrating electronic humidity meters - various salt solutions in equilibrium with an air headspace.
All the best
Rob