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Hi y'all - We are trying to figure out how "good" some of our PEGs
still are and would appreciate if anybody had any advise for a proper
assay.
Specifically, PEGs, as well as other organics, such as dioxane,
glycerol, etc., over time accumulate peroxides that are harmful to
proteins. The good old iodide test (mixing the sample with potassium
iodide/acetic acid) gives some hints about peroxides in a sample.
However, I would like to be more quantitative. Essentially, I'd like
to define a threshold value at which a chemical should be discarded,
and I'd like to have a reliable test for that. There are quantitative
kits available that use Fe++/xylenol orange. Here are the questions:
1. Does anyone actually test their chemicals for peroxides?
2. What tests would be useful for PEGs, dioxane, glycerol, and the
likes?
3. Has anyone bothered to define a threshold for 'good' vs. 'bad'?
4. Is peroxide formation a problem only for liquid PEGs, or does it
also happen to a significant degree in solid PEGs?
5. What is the best storage method for (liquid) PEGs? Does storage at
4°C or -20°C prolong the lifetime?
6. Any other thoughts?
Many thanks in advance.
Best - MM
------------------------------------------------------------------------
--------
Mischa Machius, PhD
Associate Professor
UT Southwestern Medical Center at Dallas
5323 Harry Hines Blvd.; ND10.214A
Dallas, TX 75390-8816; U.S.A.
Tel: +1 214 645 6381
Fax: +1 214 645 6353
