For those of us truly controlling types :), I used to make the PEG solutions and filter them over a Bio-Rad resin that filtered out all the junk added to stabilize the PEG solution. Then, of course I had to freeze all my PEG solutions in aliquots, or wrap them in foil and store at 4C in the dark. This would take several days, depending on the FW of the PEG. If you are really sensitive about what is in your PEG solutions, try GC-grade PEG's. The FW profile is much more restricted around the reported value (i.e. PEG 3350 molecular biology grade has a broad peak centered on Mr=3350. PEG 3350 GC-grade has a much tighter peak profile.) Back before you could buy Crystal Screen I, II or HT, you had to make the stock solutions, then make the screen. But at least when you did that, you had all the stocks. Now, I just buy pre-made solutions, and keep them in a drawer with a date opened written on the bottle. Isn't progress grand? :)
Bryan -------------------------------------------------------------------------- Confidentiality Notice: This message is private and may contain confidential and proprietary information. If you have received this message in error, please notify us and remove it from your system and note that you must not copy, distribute or take any action in reliance on it. Any unauthorized use or disclosure of the contents of this message is not permitted and may be unlawful. -----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Jacob Keller Sent: Wednesday, August 24, 2011 3:18 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Aging PEGs A while ago I measured the pH's of old and new PEGs and found them very different, and internally attributed all "old vs new PEG issues" to pH. Upon reflection, this seems too simplistic. Are there other known mechanisms of crystallization capacities of PEGs of various ages? Jacob Keller ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program cel: 773.608.9185 email: j-kell...@northwestern.edu *******************************************
