Chromatography Forum

Not strictly GC I know but it might have a bearing on this problem.

I am analysing some fabric for a client. The fabric has been treated with a solvent then left to dry. There are residual impurities left. The client claims that these are removed if left for several days at room temperature. My analysis shows that there are residual volatile material impurities left on submitted samples of fabric that have been air dried at 50°C for 30mins.

My question is (here comes the GC related bit - let's call it paper chromatography ) what is the relationship between volatility and temperature likely to be.

e.g. for every 10°C increase in temperature does the rate of volatalisation double? This happens with chemical reactions and just reflects the increased speed of molecular motion thus leading to increased chance of collision/reaction.

Could we then predict what temp/time would be required to equal 5 days at room temp (with a forced flow)? Assume that the forced flow is constant, and that we can't go over, say 100°C.

Regards and thanks in advance for any thoughts,

Ralph

Oh dear, where do I start?

Being in the chemical industry I can tell you that the extrapolation of your problem isn't easy but nonetheless possible

At our place we have a rule of thumb that every 25°C the vapor pressure of a solvent doubles.

Another rule of thumb says that 80°C with forced flow and 1 hour of exposition eliminates all residual solvents but this depends on the retention of the fabric.

Nonetheless I'd start with these conditions as we've been using these for over 20 years and nobody ever complained

And what solvent are we talking about by the way?

Hi,

Thanks, that's very useful. The solvent is industrial denatured alcohol, which obviously is removed rapidly- it is the removal of the residual higher boiling impurities that I am interested in. (and the origin of the phrase rule of thumb)

Regards,

Ralph

Regarding the origin of the term I recommend http://en.wikipedia.org/wiki/Rule_of_thumb

How is your alcohol denatured? Naphtha is no problem under the conditions I've given and neither is pyridine.

So please tell me what (other) components your denatured alcohol contains.

That way I could (possibly) tell you if the storage at room temperature is reasonable.

Any progress?

Hi,

Sorry, only just spotted your post. Some of the residual impurities that I have identified are methyl pyridine and glycols. I have passed recommendations on to my client and he is doing some more drying tests. I will be analysing them in the coming week. In case I didn't make it clear, he doesn't want any residual material left. Hopefully the residuals will have been removed/greatly reduced this time.

I was aware of the maritime connection to the phrase. There are so many that have their origins there - There'll be the devil to pay, Between the devil and the deep blue sea, Brass monkey weather etc

Thanks,

Ralph

I'm very curious how it worked out.

Hi,

I'll let you know. After scouring my old physics books I see that it boils down to (terrible pun) the Clausius-Clapeyron equation

Ralph

Hello,
maybe your client would be satisfated if you give him some experimental data. So, you have your assay results of impurities. I would prepare artificial sample with about the same content of impurities as the real sample has, leave them at the same condition and then measure.
Comparing the result of artifical sample (measured) with the weights you've done (teoretical content), you can get the recovery.
Good luck
ana