Popular LabKit · Recipe
Acetate Buffer pH 4.5: Preparation and Recipe
How to prepare sodium acetate buffer pH 4.5 at 0.05, 0.1 or 0.2 M: millilitres of glacial acetic acid and grams of sodium acetate (trihydrate or anhydrous) for 1000 mL.
Recipe: 0.1 M sodium acetate buffer, pH 4.5, 1000 mL
| Component | Amount |
|---|---|
| Glacial acetic acid (99.7%, density 1.049 g/mL) | 3.46 mL (3.623 g) |
| Sodium acetate trihydrate, CH₃COONa·3H₂O | 5.397 g |
| Purified water | to 1000 mL |
Other concentrations
| Component | 0.05 M | 0.1 M | 0.2 M |
|---|---|---|---|
| Glacial acetic acid | 1.76 mL | 3.46 mL | 6.79 mL |
| Sodium acetate trihydrate | 2.624 g | 5.397 g | 11.13 g |
| or sodium acetate anhydrous | 1.582 g | 3.254 g | 6.713 g |
Method
- Dissolve the sodium acetate in about 800 mL of purified water.
- Add the glacial acetic acid with a graduated pipette (in a fume hood; it is corrosive and has a strong smell).
- Check the pH with a calibrated pH meter and fine-adjust with dilute acetic acid or sodium hydroxide.
- Make up to 1000 mL in a volumetric flask and mix.
At pH 4.5 the buffer is about 60% acetic acid and 40% acetate. Acetate buffer hardly changes with temperature, so the same recipe works at 25 °C and 37 °C.
Recipes are calculated with the Popular LabKit buffer model (ionic strength and temperature corrected) and checked against published buffer tables. For a pharmacopoeial test, follow the reagent or buffer recipe in your monograph. Always confirm pH with a calibrated pH meter.
Frequently asked questions
Can I use 2 N acetic acid instead of glacial acetic acid?
Yes – 2 N acetic acid is 2 mol/L, so use the mmol of acid shown in the calculator divided by 2 to get mL. For example 60.3 mmol needs about 30.2 mL of 2 N acetic acid.
Is this the same as the pH 4.5 acetate buffer in dissolution methods?
The chemistry is the same, but pharmacopoeial dissolution media specify their own quantities. For a monograph test, follow the monograph recipe and use this page for routine laboratory work.
Which sodium acetate should I use?
Either. The trihydrate (MW 136.08) is the most common in Indian labs; the anhydrous salt (MW 82.03) absorbs moisture, so keep it tightly closed.