Commercial polyethylene glycol is contaminated with polymers that have aldehyde groups at the ends. Other impurities include some amount of internal epoxide linkages. The aldehyde groups can be additionally oxidized to carboxylic acids. I would assume that oxidation to terminal carboxylic acids explains the change in PEG pH vs. time. The pH will also change as the PEG solution comes to equilibrium with atmospheric carbon dioxide. The aldehyde content increases with time after the PEG is dissolved in water and stored under normal atmospheric gas. These PEGs can react with protein amine groups.
On Aug 24, 2011, at 2:18 PM, Jacob Keller wrote: > 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 > *******************************************
