Biological buffer MES potassium salt, also known as 2- (N-morpholine) ethanesulfonic acid potassium salt, is a white powder. It is a zwitterionic buffer, which is mainly used to distinguish very small proteins on bis tris gel. The pKa value of MES potassium salt is close to the physiological pH value and will not be absorbed by the cell membrane. It is basically transparent to UV light. In addition, MES is also used in cation exchange chromatography and as a biological buffer in plant cell cultures. MES is also commonly used in buffer culture media for yeast, bacteria, and mammalian cells, but it may be toxic to plants when the concentration exceeds 10 mM. MES is also a good buffer choice in various chromatography and electrophoresis experiments, as it exhibits lower ion mobility and conductivity. It is an effective buffer in the pH range of 5.5 to 6.7.