Aerosil in sample

[Mattias]

Hi,

Does anyone have experience in removing Aerosil (water-free colloidal silicon dioxide) from samples? The solutions become cloudy, and the filters (0.22 µm) get stuck immediately. Even high-speed centrifugation does not help.

[Uwe Neue]

I would acidify the sample to precipitate the colloidal silica. Watch out for loss of analytes.

[Russ]

Have you tried filters with a glass fiber prefilter?

[Mattias]

The solutions are cloudy even after flitration with 0.22 µm filters (the two drops that pass through the fliter)

I will try to acidfy the samples, haven't tried that yet. Thanks for the help!

[diana]

What about centrigation? If it is not possible to precipitate, I centrifuge my samples (5min at 4000 upm should be enough) and afterwards I use a 0.45 µ filter.

[Peter Apps]

Hi Mattias

This is going to be tricky - colloidal silicas have particles going down to molecular dimensions, and depending on the surface treatment they are macroscopically sticky.

The only thing that I can think of is to spin them through a very high MW cut off ultrafilter - the kind that is used to take proteins and other large molecules out of biological samples.

Good luck

Peter

[Mark Tracy]

You can also try Anotop+ 0.02µm filters from Whatman; that's right 20nm. They also have a glass-fiber prefilter built in.

[HW Mueller]

I have a secondary interest in this, sort of. We have had horrendous trouble with transition metal oxides (for instance Y oxides stick to everything). From synthetic organic chem. there are still these ugly memories of Al oxides. All can and could be handled after acidification, so I wonder if Uwe´s suggestion is not the way to go?

[Mattias]

I added some HCl and it worked!

The silica precipitated and floated on the surface. It was possible to filter the solution with the syringe filter (0.22 µm). Now I have to see what happens with my analyte...

[HW Mueller]

Good to know that Si oxides are similar to the others.

[Mattias]

Of course my analyte was hydrolysed as well....

Removal of Aerosil from samples must be a very common problem, since it is used in many solid pharmaceutical formulations.

Doesn't winemakers use something to remove particles from wine?

[HW Mueller]

Maybe a tight pH, time, and temp. control will do the trick? Or ionic strength changes might modify the gel so that it can be filtered?

[Mattias]

The situation has been solved! When I increased the volume of solvent, the solution could be filtrated much more easily.

I then injected 1000 µl (instead of 100 µl) on a small precolumn. By using a column switch I then eluted my peaks to the analytical column. I probably still inject particles, but it will only kill my precolumn. I see no problem the first 10 injections at least.