When working with 50 mM phosphate buffer (pH = 7.4) I have noticed a tendency of buffer salt cristalizing above the methanol concentration of 50% or so. It should depend on both, concentration of buffer and the % of organic modifier, different for MeOH, ACN, THF etc. Have you got an experience on how to predict such dangerous tendencies (once we've lost an expensive quartz cell of UV detector by this!), or perhaps some factual information about the certain limit concentrations etc.?

Thanks in advance,

Maciej Turowski
Kyoto Institute of Technology

Assuming that you are using some sort of gradient-- a quick check is to mix the highest concentration of buffer/organic in a smaller amount in a beaker. Then check for crystallization there.