Concentrating 1-2 ml to <20 uL

[Dima Klenchin]

bobjones1235 at yahoo.com (Bob Jones) wrote:

:I was wondering if anyone is aware of a product of "home-grown" method
:to concentrate solutions of macromolecules (protein, plasmid, virus,
:you name it) from ~1-2 ml to <20 uL.  I need to maintain (as much as
:possible) the native state of these species for biophysical studies so
:i'm not to keen on precipitation methods.  Most centrifuge-based or
:minicon-type concentrators seem to only get you down to ~50 ul (I no
:it doesn't seem like a big difference between 50 and 20 but it is) and
:unfortunately I don't have enough sample to take advantage of these. 
:I had thought of floating the sample on a dialysis membrane above a
:PEG solution but attempts to concentrate buffer alone didn't go to
:well :)  Any advice/input would be greatly appreciated.

In case I had to go 2 ml -> 10 ul, I'd do the following:

Concentrate in Centricon to ~  100 ul, then lyophilize and resuspend 
pellet in 10 ul H2O. If salt concentration increase is unacceptable, 
dialysis into ammonium  acetate or carbonate before lyiphilization, 
or a micro-dialysis against working buffer after concentration can be
done.  

        - Dima