sp-cation exchange column.. - phosphate /tris buffer ph 7.0 (Dec/27/2006 )

for an sp-cation exchange column.. i need to use phosphate /tris buffer ph 7.0
hw do i decide which buffer to use? is tris.. tris+ ions.. not good for the stability of the cation exchanger?
or shal i try only phosphate buffer? what molarity shud b enuf in any case?
thanku!

tris will probably bind to sp, use phosphate. phosphate should be good from 10-50mM, 20mM may be a good start.

I've been using HEPES in my SP buffers and it seems to work.