Chromatography Forum

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.

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

Have you tried filters with a glass fiber prefilter?

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!

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.

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

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

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?

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...

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

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?

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?

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.