Citric Acid – Na2HPO4 Buffer Preparation, pH 2.6–7.61
From Sigma Buffer Reference Center
Citric acid monohydrate, C6H8O7 • H2O, MW 210.14; 0.1 M contains 21.01 g/L.
Na2HPO4, MW 141.98; 0.2 M contains 28.40 g/L, or Na2HPO4 • 2H2O, MW 178.05; 0.2 M contains 35.61 g/L.
pH | x mL 0.1 M-citric acid | y mL 0.2-Na2HPO4 |
---|---|---|
2.6 | 89.10 | 10.90 |
2.8 | 84.15 | 15.85 |
3.0 | 79.45 | 20.55 |
3.2 | 75.30 | 24.70 |
3.4 | 71.50 | 28.50 |
3.6 | 67.80 | 32.20 |
3.8 | 64.50 | 35.50 |
4.0 | 61.45 | 38.55 |
4.2 | 58.60 | 41.40 |
4.4 | 55.90 | 44.10 |
4.6 | 53.25 | 46.75 |
4.8 | 50.70 | 49.30 |
5.0 | 48.50 | 51.50 |
5.2 | 46.40 | 53.60 |
5.4 | 44.25 | 55.75 |
5.6 | 42.00 | 58.00 |
5.8 | 39.55 | 60.45 |
6.0 | 36.85 | 63.15 |
6.2 | 33.90 | 66.10 |
6.4 | 30.75 | 69.25 |
6.6 | 27.25 | 72.75 |
6.8 | 22.75 | 77.25 |
7.0 | 17.65 | 82.35 |
7.2 | 13.05 | 86.95 |
7.4 | 9.15 | 90.85 |
7.6 | 6.35 | 93.65 |
For 2021 QBoC
Need pH 3,4,5,6,7
Start with
- Citric acid (100 mM) (borrowed from P-Chem)
- 2.65 g
- 125 mL H2O
- Sodium phosphate dibasic (200 mM)
- MW = 268.07
- 200 mM = 8.042 g
- 150 mL H2O
Then make
pH | x mL 0.1 M-citric acid | y mL 0.2-Na2HPO4 |
---|---|---|
3.0 | 39.725 | 10.275 |
4.0 | 30.75 | 19.275 |
5.0 | 24.25 | 25.75 |
6.0 | 18.425 | 31.575 |
7.0 | 8.825 | 41.175 |
Test pH of 1:10, 1:2
- pH remains constant when diluted to 20% with LB.
- So make 50 mL of each diluted to 40% with LB. Students will dilute it 1:1 with LB
- 20 mL buffer
- 30 mL water
- Filter steriize, aliquot for students
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