Preparation of 1M MOPS (Free Acid) Solution


MOPS (Free acid, C7H15NO4S, Molecular weight: 209.26) is a zwitterionic buffer, useful for several cell and molecular biology applications due to its pH range between 6.5 – 7.9. It is soluble in water.


Reagents and solutions
MOPS (Free acid, Molecular weight: 209.26)
Deionized or Milli-Q water

Equipment and disposables
Measuring cylinder
Conical flask / Beaker
Magnetic stirrer
Sterile filter unit (for filter sterilization)

pH 7.4

Preparation of 500 ml of 1 M MOPS, pH 7.4 stock solution


Use appropriate personal protective equipment (lab coat, gloves, goggles, etc) for your safety and follow the guidelines of your institute.

Step 1: To prepare 500 ml of 1 M MOPS solution, weigh out 104.65 g MOPS in a 1 Liter conical flask/beaker. Add 400 ml deionized/Milli-Q water. Stir until all solute is completely dissolved.

Do not dissolve in 500 ml of deionized / Milli-Q water. In most cases, solution volume increases when a large amount of solutes dissolve in a solvent.

It is always a good practice to dissolve the solute in a small volume of solvent (≈ 80% of the final solution volume). After the solute is completely dissolved and pH is adjusted, make up the correct volume with the solvent.

Step 2: Adjust the pH of the solution to 7.4 using 10N NaOH

You need to add ≈ 30 – 40 ml of 10N NaOH to adjust the pH 7.4.

You can adjust to any desired pH between 6.5 – 7.9 (MOPS pH range).

Step 2: Adjust the volume to 500 ml with deionized/Milli-Q water. Mix it again.

Step 3: Sterilize the solution by filtering through a sterile filter unit containing a membrane with porosity 0.22 µm or less. 

We don’t recommend autoclaving the solution.

Freshly prepared solution will appear clear colourless liquid which can turn into yellowish with time.

Stored the solution at 4° C in a brown bottle

Protect the solution from light.

Follow the table to prepare MOPS solutions of different concentrations and volumes.
Conc. / Volume100 ml250 ml500 ml1000 ml
10 mM0.21 g0.52 g1.05 g2.09 g
50 mM1.05 g2.62 g5.23 g10.46 g
100 mM2.09 g5.23 g10.46 g20.93 g
0.5 M10.46 g26.16 g52.32 g104.63 g
1 M20.93 g52.32 g104.63 g209.26 g 



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