PBS buffer - Salt precipitation? (Mar/21/2009 )
Be sure you use good water to dissolve the salts of 10x PBS.
After autoclave sterilization I once saw a precipitate! It seems that the DI water installation has broken down and my water contained to much carbonates or something!
At 4 degrees celsius your salts precipitate and form christals. Heat it up again and they dissapear.
are you sure that the glassware that you stored it in is not contaminated with cations or detergents?
if there is calcium present (from rinsing with tap water instead of deionized, or if the deionizer is exhausted) then you may be seeing calcium phosphate precipitating (or magnesium phosphate if it was heated).