Urea-containing buffers: How long can I store them?

[Viraj Master]

Hello all,

I am using the Qiagen pQE series of vectors to express proteins.  There
are two buffers which I use a lot, Buffer B and Buffer C.

These contain:
8M urea 
0.1M NaH2PO4
0.01M Tris 

Buffer B is at pH=8
Buffer C is at pH=6.3

I have been told that I must make these buffers up **fresh** each time
prior to use.  I would like to be able to prepare batches of these
buffers and store them.  Does anybody know whether this can be done and
not affect the protein prep?  If so, are they stored in the cold, or at
room temp?  For how long can they be stored?

Many thanks,

Viraj

Viraj Master PhD
Dept of Organismal Biology
University of Chicago