Also, just for fun, check the pI of your protein and make sure the pH of your buffers is right for the pI.
You could also try different pH in your search for optimum conditions.
Thanks so much!! Actually, I'm trying to purify a novel protein that was discovered in our lab. Expasy has a tool that characterizes proteins for its stability based on its amino acid sequence. It characterizes our protein as being unstable. Also, the theoretical pI of our protein is reported to be 8.40. I've heard that there are different programs to calculate theoretical pIs of proteins. What are the other programs that could help in identifying the theoretical pI?