Description: MES (2-(N-morpholino)ethanesulfonic acid) is used as a buffering agent. It has pKa value of 6.15 at 20°C. The pH (and pKa at ionic strength I≠0) of the buffer solution changes with concentration and temperature. MES is highly soluble in water. The melting point is approx. 300 °C. MOPS is a similar pH buffering compound which contains a propanesulfonic moiety instead of an ethanesulfonic one.