yes, you are talking about the cobalt resin from Clontech right? We used it very successfully with a His-Asn tag, but its binding of a straight His-His tag was not so good in our hands. what would you like to know?

Thank you Guy. We are also trying to purify a his tag protein expressed in Ecoli. I am told Talon column with Co is good for purity but not very good for yield. Also we did try a Ni column but it didn't work very well for us. We are using immidazole containing buffer at different molarities for binding, washing and eluting. I am trying to know from people like you about your own experience of purity vs yield as well as any tips to improve the yield. Thank you. Vijay

It sounds like you are following a logical optimization procedure. When you say the Ni column didn't work, do you mean poor yield, or contamination from other proteins? Did you compare how much protein was in the original cleared lysate with what flowed through and what eluted at the different imidazole concentrations? (in other words, do you have a problem with affinity or specificity)