MOPS

The other mops [1]

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, MOPS is an good buffer for many biological systems at almost neutral pH. HEPES is a chemically similar pH buffering compound.

Recipe for 10x MOPS buffer

chemical structure of MOPS, 3-(N-morpholino) propanesulfonic acid

• 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 [2]. 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

External links

• Wikipedia MOPS
• MOPS recipe at Fermentas
• premade MOPS 10x from Sigma
• CSH Protocols MOPS