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Oxygen
The formation of polyacrylamide gels proceeds via free radical polymerization.
The reaction is therefore inhibited by any element or compound that serves
as a free radical trap (Chrambach 1985). Oxygen is such an inhibitor.
Oxygen, present in the air, dissolved in gel solutions, or adsorbed to
the surfaces of plastic, rubber, etc., will inhibit, and in extreme cases
prevent, acrylamide polymerization. Proper degassing is critical for reproducibility.
Therefore, one of the most important steps in the preparation of polyacrylamide
gels is the evacuation, or degassing of gel solutions immediately
prior to pouring the gel. This is done by placing the flask of gel solution
in a vacuum chamber or under a strong aspirator. In some cases, a vacuum
pump may be required.
Buffer stock solutions and monomer stock solutions are usually stored at 4C. Cold solutions have a greater capacity for dissolved oxygen. The process of degassing is faster and more complete if the gel solution is brought to room temperature (2325C) before degassing begins. Furthermore, if a cold gel solution is placed under vacuum, the process of evacuation tends to keep the solution cold. Pouring a gel with a cold solution will have a substantial negative effect on the rate of polymerization and on the quality of the resulting gel.
Polymerization in which riboflavin is used as one of the
initiators calls for degassing. The conversion of riboflavin from
the flavo to the leuco form (the species
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