Hi there,
I'm currently doing research on the compsition of the liquid phase generated by thermal degradation of Poly(methyl methacrylate) (PMMA).
In my group we are especally interested in finding the monomer methyl methacrylate (MMA).
But from literature I have kind of a clue what else I can expect to be in the mixture,
like methyl propionate, methyl isobutyrate and other carbonyl-, ester- and diester-compounds.
Their boiling points should range between 50 °C and 270 °C and I consider them themally stabel.
Now I thouhgt on first analyzing the samples with GC-MS, because the GC allows to seperate the different compunds and MS will help me to characterize those compounds.
The problem is, that I've never done GC-MS before and I'm a bit puzzled if I have to dissolve my sampels or if I can probe them directly?
Is there a benefit in using a solvent?
And what requiremnets should a solvent fullfil, apart form dissolving my sample and beeing thermally stable, especally regarding the boiling point?
Thanks already for your suggestions!
Hello Christoph
You have already mentioned the most important criterion: all analytes should dissolve in the solvent without any problems. I think methanol would be a good choice. Since GC-MS systems usually have a high sensitivity, it makes sense to dilute the sample. You can determine the dilution factor yourself. I would prefer a split injection at this point, since residual monomers are mostly volatile and can therefore not be focused well at the column head. The split ratio can easily be adjusted to the concentration of the injection solution at this point (high concentration = high split ratio). The temperature program is column-dependent. Since I don't know which phase is installed in your GC, I can't say much about it, but optimizing a separation is not big a problem.
In my experience the mass range of the MS is optimal with 35-350 u, no residual air peaks are recorded and the high siloxane masses of the column bleed are also not recorded. Methanol as solvent has the advantage that it is also "invisible" with mass 32.
Otherwise, additional information would be useful, e.g. which instrument (manufacturer), which column, sample quantities, autosampler, etc.
If you have more questions I will look for helpful answers.
Good luck and many greetings from Krefeld
Joachim Horst
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