The 5X western blot protein loading buffer is used to detect sample migration on the gel. It is also used to load any empty lanes on the gel during gel electrophoresis to ensure that samples do not diffuse from one well to another.
Composition
12 % glycerol by volume; 60 mM Na2EDTA pH 8; 0.6% by weight SDS; 0.003% by weight bromphenol blue