MOPS (3-(N-morpholino)propanesulfonic acid) is a buffer introduced in the 1960s, one of the twenty Good's buffers. It is a structural analog to MES,[1] and like MES, its structure contains a morpholine ring. HEPES is a similar pH buffering compound that contains a piperazine ring. With a pKa of 7.20, MOPS is an excellent buffer for many biological systems at near-neutral pH.
MOPS is frequently used as a buffering agent in biology and biochemistry. It has been tested and recommended for polyacrylamide gel electrophoresis.[2] Usage above 20 mM in mammalian cell culture work is not recommended.[3] MOPS buffer solutions become discolored (yellow) over time, but reportedly slight discoloration does not significantly affect the buffering characteristics.[4]