Glycerol in SDS-PAGE

Glycerol is added to the loading buffer to increase the density of the sample. It is more dense than water allowing it to act as a weight on the sample. This causes the sample to fall to the bottom of the well when loaded into the gel, preventing it from diffusing into the running buffer. If the sample starts to float up in the well, more glycerol can be added to the sample without affecting the proteins themselves.