The gels typically consist of acrylamide, bisacrylamide,
the optional denaturant (SDS or urea), and a buffer with an
adjusted pH. The solution may be degassed under a
vacuum to prevent the formation of air bubbles during
polymerization. Alternatively, butanol may be added to the
resolving gel (for proteins) after it is poured, as butanol
removes bubbles and makes the surface smooth [10]. A
source of free radicals and a stabilizer, such as ammonium
persulfate and TEMED are added to initiate
polymerization [11]. The polymerization reaction creates a
gel because of the added bisacrylamide, which can form
cross-links between two polyacrylamide molecules. The
ratio of bisacrylamide to acrylamide can be varied for
special purposes, but is generally about 1 part in 35. The
acrylamide concentration of the gel can also be varied,
generally in the range from 5% to 25%. Lower percentage
gels are better for resolving very high molecular weight
molecules, while much higher percentages are needed to
resolve smaller proteins.