Is there anybody who knows methods to detect polysiloxane-based anti-foaming agents in beverages?
Thanks a lot.

This is not a GC or HPLC method, but I believe that siloxane has a strong IR absorbance band at about 1261 cm-1. You can try extracting the beverage with chloroform and maybe toluene and then scanning in the infrared in a fixed pathlength cell. You should look at the USP method for dimethicone in dimethicone tablets (I think that this is the proper monograph). The method is very sensitive and can even be made more sensitive by evaporation of the solvent and redissolution of the silicone oil in a small volume of the solvent. I have done this very successfully as a cleaning validation method.

How about ICP for total silicon? Compare to silicon content of antifoaming agent.

I think that total silicon is a problem. When I was looking into other ways to do the dimethicone assay for the cleaning validation, and another application, the people that I talked to about using ICP said that, becuase of the problems with silicon, the assay would not be very accurate. This was ten of so years ago, so probably things have changed. It would probably be worth investigating.

PS:? mmaxxxx: If you want to e-mail me with a phone number I would be glad to tell you more about how we did it by IR.

Chris

I think the problem with measuring silicon is that aqueous solutions will dissolve silicic acid from the walls of any glass vessels they're held in.

Mmaxx,
The siloxanes are the smaller rings. They are easy do on GC. MS is silicone selective as is one of DET's detectors.
Jim

Thanks to all!
I'll start with some FT-IR attempts, then (if it doesn't work) with some AA.
Bye.
MMAXXXX