MOPS



MOPS is the common name for the buffering compound in MOPS buffer. MOPS stands for 3-(N-morpholino) propanesulfonic acid, and with a pKa of 7.20, makes a good buffering agent for many biological systems requiring neutral pH. HEPES is a chemically similar pH buffering compound.

Recipe for 10x MOPS buffer, 1 L



 * 83.7 g MOPS; MW 209.3 g/mol
 * 13.6 g Sodium Acetate, trihydrate; MW 136.1 g/mol (watch out: NaAc, anhydrous is only 82 g/mol or 8.2g)
 * 3.7 g EDTA, disodium dihydrate; MW 372.24 g/mol (again check MW of the salt you stock)


 * add 800 ml of nuclease free distilled water; mix to dissolve
 * adjust to pH 7 with NaOH (prepared in nuclease free distilled water)
 * fill to the final volume of 1000 ml


 * filter sterilise or autoclave
 * store at room temperature
 * protect from light; do not use if the solution is dark (yellow is ok)

Final concentration in 10x stock

 * 400 mM MOPS (buffering)
 * 100 mM NaAc
 * 10 mM EDTA (nuclease inhibition by Mg2+ chelation)

Variation
Some protocols use a less concentrated MOPS buffer
 * 200 mM MOPS - 41.9 g in 1 L
 * 20 mM NaAc - 2.7 g
 * 10 mM EDTA - 3.7 g

Stability of MOPS
Contrary to common belief, MOPS is sufficiently heat-stable to be autoclaved. Solution will turn yellow but this does not interfere with its buffering capacity. See, for example, Farrell RNA methods, p201. Straw coloured buffer is good but do not use darker buffer.

Some OWW protocols which use MOPS

 * Jacobs:Protocol RNA Agarose Gel
 * Knight:NuPAGE electrophoresis
 * Sauer:bis-Tris SDS-PAGE, the very best