Chromatography Forum

Hi,
Does anyone know a good method for analysis of dipropylene glycol?
Its not very volatile is it??!!
I have tried GC-MS with m/z 59 but I have many co-elutions in my sample.
Is there a good derivatization I can perform? (I have FID and MS).
Many thanks in advance.
WK

Dipropylene glycol by capillary GC will give several peaks; we've used PEG-type columns for it (MS or FID) from aqueous solutions, but most often we dissolve the sample in DMF and derivatize with BSTFA and use an HP-1 or HP-5 type capillary with FID or GCMS. Again, several peaks will be present, quantitate by summing the areas or using automated area summation. For identification of glycol ethers, the trimethylsilyl derivatives oftentimes give GCMS patterns easier to match up with your search libraries than running non-derivatized. We do this stuff all the time here.

I have prepared acetate esters of this compound as well. See any good book on derivitization methods to see how it is done. Not difficult. You can have isomers, which accounts for the multiple peaks, either derivitized or underitized. I have done both.

Thanks for the replies!
Consumer Products Guy:
I propose to do the derivatization in hexane with BSTFA - is this OK?
What is DMF fully?
WK

DMF is N,N-dimethylformamide. I've never tried trimethylsilyl derivatizations in hexane, we use more polar solvents because the stuff we want to derivatize has polar (hydroxyl) groups. I don't know offhand if DPG is even soluble in hexane. Pyridine usually works well as silylation solvent but has its characteristic nasty smell. I remember using ethyl acetate as derivatizing solvent as well.

BSTFA does not require a solvent to derivitize a glycol, which are quite reactive. Diluting, especially with a non-proton scavenging solvent, may inhibit completeness and/or the stability of the reaction products.

WARNING: Due to the small size of the TMS-DPG it may be difficult to separate it from residual BSTFA.

It is possible to use Acetic Anhydride and pyridine to derivitize. If feasible extract and consume the excess AA with hexane-methylene chloride and salt water.

But I would not go so far to claim one is better than the other. You should know what options you have available to you. I hope I have been helpful.

There is no problem separating DPG from the BSTFA; even propylene glycol-TMS or ethylene glycol TMS. I haven't been able to separate stuff like PG methyl ether from the BSTFA. I don't usually "intentionally" add solvent such as DMF, that's just the sample dissolution solvent.

Thanks for the info CPG. It sounds like the BSTFA is a lot more pure than when I used to use it 25 years ago. Once it was hard to see anything at trace levels due to the 'crop' of tiny peaks early in the chromatogram.

thanks again for your information.

Thanks for the help C1 and CPG.
I got some reagent in and the reaction is very nice.
I am determining the level of detection now.
WK