I am preparing CsCl solution for ultracentrifuge. The concentration suggested by the protocol is 1.4 mg/mL in 10 mM Tris-HCl, pH 8.0. I weighed the salt and added the Tris buffer while stirring. Because CsCl absorbs heat when dissolving, I heated the solution to 60 C. It worked alright; however, once I removed the beaker from the heating plate, precipitation started. The amount of precipitation is so large in the end that I don't think the buffer can be used at all.

1.4 mg/mL is lower than the solubility of CsCl in water at 25 C (1910 g/L). However the existence of Tris added into the complexity. Has anyone experienced a similar situation?