Preparation of 1M MOPS (Free Acid) Solution

Overview

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.

REQUIREMENTS

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)

Composition
1 M MOPS
pH 7.4

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

PROCEDURE

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.

Precaution
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.

Tip:
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

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

Tip: 
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. 

Precaution:
We don’t recommend autoclaving the solution.

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

Storage
Stored the solution at 4° C in a brown bottle

Precautions
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 

REFERENCES

Goldbio: https://www.goldbio.com/documents/3551/MOPS+Buffer+1M+Stock+Solution+with+table.pdf

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