problems with phosphate buffer in hydroxyl apatite chromatography - (Jun/04/2007 )

Hi

I am using 0.5M sodium phosphate buffer to purify proteasome using hydroxyl apatite chromatography. I do the purification in 4deg. I am constantly having problems with this buffer which crystallizes after standing for a while in the cold cabinet. I allowed the crystals to go into solution after bringing to room temperature. But the problem continues as i made a fresh buffer (titrating monobasic and dibasic).
Can somebody help me out?

Thanks

we use potassium phosphate for our hydroxylapatite columns. it doesn't crystallize at cold room temperatures like sodium phosphate does.