I have a sample that is polymeric and am looking for the amount of residual solvent and monomer. The material is very non-polar with a mol weight of 2K and a melting point of 85 C. Would this analysis lend itself better to headspace or P&T? I am new to P&T, is it only for aqueous samples?

Headspace sampling is the right choice. You should thermostat the sample at > 90 °C to ensure a melt, or dissolve the polymer in a higher-boiling solvent that will not interfere with the separation of monomer and residual solvent: dimethylformamide or DMSO may be good choices. Calibrate by the standard addition method, since it is unlikely you can obtain a polymer sample with no solvent or monomer.

You should use a constant thermostatting time for the best reproducibility. Also, be aware that the monomer may polymerize at the elevated thermostatting temperature.

Multiple Headspace Extraction (MHE) is an alternative to standard addition calibration, but this will require at least 2, preferably 3 extraction cycles per sample.

The PerkinElmer Instruments TurboMatrix HS samplers are a good choice with all the above capabilities.

John Hinshaw
ChromSource, Inc.

Ok, but if say I wanted to dissolve the material in hexane, could I then use a purge and trap to look at the solvent and monomer? If so, what is the accepted method for doing it this way

That depends on the type of purge and trap, or how you define purge and trap. If you mean a P&T system that sparges (bubbles) gas through a liquid solution into an absorbent trap, as in VOA water analyis, then you may encounter some problems with the polymer clogging the sparger, even if you use a needle sparger instead of a frit.

If you mean a system in which gas purges the headspace over your polymer (in solution) into an adsorbent trap, you're still better off with regular equilibrium headspace, because the large amount of hexane or other solvent present will overload the trap and potentially break through during sampling.

Equilibrium headspace sampling is the technique to which I referred obliquely in the above message -- the sample is sealed in a vial and thermostatted, allowed to reach distribution equilibrium between the gas phase and liquid phase; then an aliquot of the gas phase is withdrawn, either directly into the column or via a gas sampling valve loop. There's no trap to get in the way. The only reason to have a trap there is to get down to low ppb trace levels.

In any case, hexane may not be a good choice because you'll have to separate it from solvent and monomer in the GC. A high-boiling solvent will elute after solvent and monomer, and just requires a quick temperature ramp and/or pressure ramp to push out. If you want to get really fancy, you can arrange to backflush the heavy solvent off the column, too.

-- John

We have some experience in that field, please contact me via e-mail
c.z42@gmx.net

Many thanks for all the information John. I have arranged to purchase the PE instrumentation you mentioned above as they fit nicely with our Autosystems we are already running for standard analyses.

Let me know if you need any assistance with your equipment after it arrives.

John Hinshaw
ChromSource, Inc.