I have obtained crystals in Hampton Crustal Screen 2, condition 26.The condition has the following components:
1. 0.2 M ammonium sulphate
2. 0.1 M MES buffer pH 6.5
3. 30% PEG mononmethyl ether 5,000.
When I try to prepare the screen in-house, I use the Hampton stocks of 3.5 M ammonium sulphate and 50% PEG mononmethyl ether 5,000. I make the MES buffer using MES hydrate, SigmaUltra from Sigma and maintain the pH accurately. The water I use is filtered MilliQ. However, the PEG MME and the rest of the solution remains immiscible and thus, forms droplets of separated PEG when I set up crystallization. The original condition from Hampton has no such problems and gives good crystals.
Can anyone let me know how to overcome the problem insolubility of PEG MME in the buffer mix? I have not faced such problems with other conditions which I prepare in house and have PEG in them. Further, it's not possible for me to use the original screen all the time.