Dimethicone contamination of glass

[MestizoJoe]

I'm working in a lab that analyzes lots of dimethicone.

something has been contaminating our glass and ruining our meniscus in volumetric flasks. I think it is dimethicone but I'm not sure. I know that soaking glass in 10% nitric acid overnight removes this film and gives us back our meniscus.

Has anyone worked with dimethicone and noticed this? If so, are there other less harsh ways to remove the contamination?

Thanks

[paulw]

I know that for dimethicone analysis we actually used teflon sep funnels because it would adhere to the glass sep funnels and thus make the assay inconsistent. The stuff is a pain to clean off of manufacturing equipment also. It might be worth your time to try a dilute citric acid solution, I know that they used that in production to clean the stainless steel equipment. They also used an alkaline cleaner. The alkaline bath would likely be more harsh to the glassware and potentially the technicians than the 10% nitric acid.

[carlos.teixeira]

As there are risk of volumetric flasks damaging, Joe, you should send them to new calibration before their use. Also, change glass for plastic flasks. Hoping your best, Carlos de Souza Teixeira - teixeiracs@yahoo.com

[MestizoJoe]

For flasks which have grease visibly at the bottom, hexanes will remove the excess grease but it won't remove it from the surface of the glass and I still have a flat meniscus. So far only 10% nitric acid has worked to restore a nice meniscus. I used 10% citric acid and it didn't work. I think using plastic volumetric flasks is a good idea.

I'm still hoping to find an inexpensive way to clean the glass. Thanks.

[Consumer Products Guy]

Dimethicone and silicones are more soluble in chlorinated solvents like chloroform or CH2Cl2, so I might try those.

[bluejay]

We have had luck cleaning something silimar with a long (1-2 days) soak in a liquid soap solution such as Liquinox in water, then washing either manually or in a laboratory dishwasher. Using liquid soap rather than powdered soap seems to make a difference.

[chromatographer1]

CPG and Bluejay have excellent suggestions.

I would consider 'Dawn' brand of liquid soap.

Followed by DCM rinse, then a methanol rinse, from my limited experience.

best wishes,

Rod

[jennyweck]

We also analyse for dimethicone in our lab. We disperse our product in MIBK so glass flasks are our only real option. We clean them with 10% nitric. Because the products we analyse also have some other oils in them, we do a rinse with heptane as well.
We generally keep our glassware segragated too. We have separate glassware for methods that use water as the solute than for methods that use other solvents.