Chromatography Forum

We have been looking at this compound on HPLC but sensitivity is low. we have (slightly old) LC-MS which needs some parts to get up and running again.

we also have GC-MS (agilent 6890) which would be a lot more straightforward in terms of resurrecting, so we've contacted our colleagues on another campus and asked them to run this compound on their own GC-MS, to see if it volatilises.

My question... is vapour pressure dictated by molecular mass, or are there other factors at play?

what's the best way to establish the volatility of a compound?

thanks in advance

Generally, volatility is a factor of the molecular weight and/or the polarity of the molecule. Oftentimes hydroxyl groups or -NH groups can be derivatized to trimethylsilyl derivatives to make them more volatile (adds weight, but decreases polarity).

Trimethlsilylation removes the possibility for hydrogen bond formation.

Molecular weight is part of the story. Thermal stability is another part of the story. Decabromodiphenyl ether will go through a GC/MS system - but the big problem is getting it onto the column. The compund will thermally degrade. But with a molecuar weight just under 1000, this compound can be run through a GC. Supposedly aflatoxin can be run through a GC - but it requries on-column injection because it will not survive the hot GC inlet. (It has been a few years since I researched that one - and someone may have been clever enough to find a way to get aflatoxin to surfive a GC inlet.).

To make a long story short - you can volatilize anything - if you do not destroy it first. Derivitization will make the compund more volatile, protect the compund from decomposition, or both.

If you can post what kind of compund you are looking at, perhaps someone will have had some experience with it.

So, what is the best "predictor" variable of retention time for a set of similarly structured and polar-ed compounds? Is it their distinct 'boiling points' or their "vapor pressures" or some other factor?

There are attempts at predicting retention times that have been around in the literature for a number of years. Retention time depends not just on vapor pressure, but also on the partition coefficient between the stationary phase and the vapor state - thus we use various stationary phases. Thus you need to be able to predict (directly or indirectly) the heat of vaporization from the particular stationary phase. I wish I could give you some good references off the top of my head, but I dumped the file that I was keeping on that about ten years ago, when I changed jobs.