BAM R61: 0.02 M Phosphate Saline Buffer (pH 7.3-7.4)
January 2001
Prepare stock solutions of 0.2 M mono- and disodium phosphate in 8.5% salt solutions and dilute 1:10 for preparation of 0.02 M phosphate saline buffer.
Stock solution 1
| Sodium phosphate dibasic anhydrous Na2HPO4 (anhydrous) (reagent grade) |
28.4 g |
|---|---|
| NaCl (reagent grade) |
85.0 g |
| Distilled water to make 1 liter | |
Stock solution 2
| Sodium phosphate monobasic monohydrate NaH2PO4·H2O (monohydrate) (reagent grade) |
27.6 g |
|---|---|
| NaCl (reagent grade) |
85.0 g |
| Distilled water to make 1 liter | |
To obtain 0.02 M phosphate-buffered saline (0.85%), make 1:10 dilutions of each stock solution.
For example:
| Stock solution 1 | 50 ml | Stock solution 2 | 10 ml |
|---|---|---|---|
| Distilled water | 450 ml | Distilled water | 90 ml |
| Approximate pH, 8.2 | Approximate pH, 5.6 | ||
Using pH meter, titer diluted solution 1 to pH 7.3-7.4 by adding about 65 ml of diluted solution 2. Use resulting 0.02 M phosphate saline buffer solution in the lysostaphin susceptibility test on S. aureus.
NOTE: Do not titer 0.2 M phosphate buffer to pH 7.3-7.4 and then dilute to 0.02 M strength. This results in a drop in pH of approximately 0.25. Addition of 0.85% salt after pH adjustment also results in a drop of approximately 0.2.
Original Source: Bacteriological Analytical Manual, 8th Edition, Revision A, 1998.