OVERVIEW
Sodium Phosphate Buffer is a widely used biological buffer (buffer range: 5.8 – 8.0). Usually, It is prepared by mixing 1M stock solution of monobasic and dibasic sodium phosphate solution.
To prepare 1L of 1M Sodium Phosphate Buffer of pH 7.2, mix 280 ml of 1M Sodium phosphate monobasic and 720 ml of Sodium phosphate dibasic.
REQUIREMENTS
Reagents and solutions
1M Sodium Phosphate Monobasic (NaH2PO4)
1M Sodium Phosphate Dibasic (Na2HPO4)
Equipment and disposables
Measuring cylinder
Magnetic stirrer
pH meter
COMPOSITION
1 M Sodium phosphate buffer, pH 7.2
OBJECTIVE
Preparation of 100 ml of 1M Sodium phosphate buffer, pH 7.2
PREPARATION:
Use personal protective equipment (lab coat, gloves, goggles, etc) for your safety and follow the guidelines of your institute.
Step 1: In a 1L measuring cylinder, take 28 ml of 1M Sodium phosphate monobasic and 72 ml of 1M Sodium phosphate dibasic.
Step 2: Mix and check the pH. pH should be 7.2.
Reasons why pH is not 7.2:
- The pH meter is not working. Calibrate your pH meter.
- The molarity of the stock solution of Sodium phosphate monobasic and Sodium phosphate dibasic is incorrect. Both Sodium phosphate monobasic and Sodium phosphate dibasic are hygroscopic and absorb atmospheric water and turn into hydrated forms that result in lower solution molarity.
If pH > 7.2: Add Sodium phosphate monobasic to adjust the pH 7.2
If pH < 7.2: Add Sodium phosphate dibasic to adjust the pH 7.2
Step 3: 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).
STORAGE
Solution can be stored at room temperature.
| Follow the table to prepare 1M Sodium phosphate buffer, pH 7.2 of different volumes. | ||||||
| Ingredients / Volume | 10 ml | 50 ml | 100 ml | 250 ml | 500 ml | 1000 ml |
1M Sodium phosphate monobasic | 2.8 ml | 14 ml | 28 ml | 70 ml | 140 ml | 280 ml |
1M Sodium phosphate dibasic | 7.2 ml | 36 ml | 72 ml | 180 ml | 360 ml | 720 ml |
