boiling point of n-paraffines under high vacuum

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
Hello everyone,

I might be asking the impossible, but I was wondering if there is a model to convert atmospheric boiling points of n-paraffines to boiling points under high vacuum. Or if there if these values are known.

I am working with a DT-MS (direct temperature resolved MS) and I want to calibrate the pyrolysis probe temperature with a n-paraffine standard (up tp C40). Because now I can only change the current of the filament, without knowing the temperature.

I also realise that it might not be possible to exactly know the temperature with this calibration method. However, it would be nice to have some indication of the probe temperature when I'm analysing samples.
There is nothing magical about a boiling point - it is simply the temperature at which the vapour pressure is the same as the ambient pressure, so how are you going to use it to calibrate temperature ? - there is no way that you will see it boil off the filament, all you will see is a smooth rise in the abundance of the ions.
Peter Apps
Thank you for the reply,

My plan was to look at te retention times of the paraffines against the current of the probe. I am now ramping the current of the probe from 0 to 1.6 A, but I don't know the temperature of the filament. Therefore, I would like to make a rough estimation of its temperature by using the maxima of the peaks from the chromatogram and/or the molecular ion peaks (which I think correspond with the boilingpoints of the components in vacuum).

If you guys suggest a different method to do this. Feel free to reply!
Assuming that you have an excess of the alkane on the filament then its signal intensity will just keep increasing with temperature - it will not be a maximum at the BP. If you have insufficient alkane then its signal will rise with temperature until it is all evaporated, which might happen before the filament reaches the BP.

In short - it is not going to work.

Peter
Peter Apps
4 posts Page 1 of 1

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