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  5. BAM R61: 0.02 M Phosphate Saline Buffer (pH 7.3-7.4)
  1. Laboratory Methods (Food)

BAM R61: 0.02 M Phosphate Saline Buffer (pH 7.3-7.4)

Reagents Index for BAM

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.

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