The document provides instructions for preparing sodium phosphate buffers at different pH levels. It describes adding specific volumes of 1M sodium phosphate stock solutions to water according to a table, adjusting the pH with NaOH or phosphoric acid if needed, and diluting the solution to a final volume of 50mL in a volumetric flask. The buffers are intended to be 0.1M solutions of sodium phosphate at pH levels ranging from 5.8 to 8.0 at 25 degrees Celsius.

1. Preparation of Sodium Phosphate Buffers
1) In a beaker pipette aliquots of 1M stock solutions according to the desired pH of your
buffer (see table below).
2) Add water to bring the volume to approximately 45 mL.
3) Measure the pH of the solution. If it is below the desired pH add NaOH to raise it to the
correct pH. If it is above the desired pH add phosphoric acid to lower it to the desired
pH.
4) Carefully pour the solution into a 50 mL volumetric flask and add water to bring the total
volume to 50 mL.
Preparation of 0.1 M Sodium Phosphate Buffer at 25 °C
pH Volume of 1 M Na2HPO4 Volume of 1 M NaH2PO4
5.8 0.40 4.56
6.0 0.60 4.4
6.2 0.89 4.11
6.4 1.28 3.73
6.6 1.76 3.24
6.8 2.32 2.69
7.0 2.89 2.12
7.2 3.42 1.58
7.4 3.87 1.13
7.6 4.23 1.78
7.8 4.48 0.52
8.0 4.66 0.34
References
Sambrook J.; Russell D.W.; Molecular Cloning: A Laboratory Manual; Argentine, J., Irwin, N.,
Janssen, K.A., Curtis, S., Zierler, M., McInerny, N., Brown, D., Schaefer, S., Eds.; Cold Spring
Harbor Laboratory Press: New York, 2001; pp A1.5.