Chromatography Forum

I am an experienced chromatographer who has run into a difficult problem.

I'm trying to determine the precise nature of a trimethoxy alkyl silane in an aqueous matrix. This means that the silane is hydrolyzed, and I'm dealing with (OH)3-Si-R (mono) or (OH3)-Si-R-Si-(OH)3 (bis). There are also significant amounts of glycol couplers and organic acids in the fluid.

I can't extract/evaporate to solids, b/c the silane polymerizes to polysiloxane upon drydown. L-L or solid phase extraction is difficult for the same reasons.

Bottom line...I'd like to do a direct determination via GC/MS, but the silanols are so active I do not see any peaks on a DB-5 type column. I'm assuming these compounds are just not eluting or being trapped in the liner.

Typical derivitization with TMS reagents is out due to the aqueous matrix.

Anybody have experience or ideas that could help me out????? Any input would be greatly appreciated.

THANKS!!!

g-star,

Probably very little help but all I can offer. Contact Corning. Saw them present on siloxanes (since that is what they do) and the issues associated. I will dig and see if I can find who presented if you want me to.

Best regards.

Thanks for the reply, I might end up having to do that.

I am truly stumped by this one.

Thanks for the reply, I might end up having to do that.

I am truly stumped by this one.

It's difficult surely. One possibility is to increase the temperatures of linner and the column to prevent the adsorption?

It is entirely possible that the silanols polymerize immediately, and that you never will see them. This is the assumption in many other reactions; look up the Dow documents on silicone chemistry. And if they are "free" they may not be very volatile. And a hot injection port is going to encourage additional reactions. Bad news all the way around, I think.

One other trick you could try that worked for me many years ago. Yes, the derivatizing reagents react with water. So just add enough to react with all the water, and have some left over to react with the other things. It is a gross mixture, but might work.

Another possibility is to remove the water using dimethoxypropane, which reacts with water to form methanol and acetone. If those don't interfere, maybe you can get it to work.

Tricky

Contacting DoW or similar might be a good idea. Also I think GC in general is out of the question as technique.

Seems to recall SPE catridge extractions with LC that can work.

Found a link to an article, unsure if it helps, the author seems to have worked with DoW.

Quote:"Using ENV+ sorbent, samples of dimethylsilanediol Me2Si(OH)2, methylsilanetriol MeSi(OH)3, were recovered from aqueous medium with excellent efficiencies (99 and 94 %, respectively). "
So perhaps?



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