Preparation of 3 M Sodium Acetate (CH3COONa) Solution, pH 5.2

OVERVIEW
Sodium acetate is a sodium salt of acetic acid which dissolves readily in water. It is commercially supplied as both anhydrous (molecular weight: 82.03) and trihydrate (molecular weight: 136.08) forms and both can be used to prepare 3M Sodium acetate solution. Since anhydrous sodium acetate absorbs water from the atmosphere, weighing it accurately is difficult as exposure to air can cause anhydrous sodium acetate to turn to hydrated form.

Here we show a procedure to prepare 100 ml of 3M Sodium acetate, pH 5.2 from sodium acetate anhydrous. Briefly, to prepare a 100 ml solution of 3M Sodium acetate of pH 5.2, dissolve 24.61 g Sodium acetate anhydrous in 80 ml water, adjust the pH 5.2 using acetic acid, and then make the final volume to 100 ml. Remember that this solution act as a buffer solution (Acetic acid-Sodium acetate buffer)

REQUIREMENTS

Reagents and solutions
Sodium acetate, anhydrous (CH3COONa) (Molecular weight = 82.03)
Deionized / Distilled water

Equipment and disposables
Measuring cylinder
Conical flask / Beaker
Magnetic stirrer
Spatula

COMPOSITION
3 M Sodium acetate

OBJECTIVE
Preparation of 100 ml of 3M Sodium acetate solution, pH 5.2 in water from sodium acetate anhydrous (CH3COONa)

PREPARATION:

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

Step 1: To prepare 100 ml aqueous solution of 3M Sodium acetate (CH3COONa) solution, weigh out 24.61 g of Sodium acetate (Molecular weight = 82.0343). Transfer to 250 ml beaker/conical flask. Add 80 ml of deionized / Distilled water. Mix until sodium acetate dissolves completely.

Note
Anhydrous sodium acetate readily converts to hydrated forms due to its hygroscopic nature.

Tip
One can use manual shaking using a glass pipette to mix the ingredients. Magnetic stirrer makes the dissolving process easy and convenient.

Precaution
Do not dissolve in 100 ml of deionized / Distilled water. In most cases, solution volume increases when a large amount of solute dissolves in the solvent.

Step 2: Adjust the pH to 5.2 with glacial acetic acid.

Precaution:
Since pH depends on temperature, one should adjust pH at room temperature (25°C).

Step 3: Adjust the volume to 100 ml with deionized / Distilled water. Mix it again.

Note:
The solution will appear colorless and transparent.

Step 4: Transfer the solution to an autoclavable bottle. Sterilize the solution by autoclaving (20 minutes at 15 lb/sq.in. (psi) from 121-124°C on liquid cycle).

Tip:
Depending on the consumption, one can make small aliquots of the solution.

Note:
One can sterilize a solution by passing through 0.2μ filter unit. Filter sterilization removes all suspended particles with size more than 0.2 μ which includes most bacteria and their spores but not mycoplasma. However, it does not inactivate enzyme activities (e.g., DNases). Autoclaving inactivates most enzymes except some (e.g., RNases) and kills most microorganisms including mycoplasma.

STORAGE
Solution can be stored at room temperature.

APPLICATIONS

• Precipitation of nucleic acid (DNA and RNA)
• Buffer solution
• Protein crystallization