To describe the preparation of 25X Phosphate Buffered Saline (PBS) for use as a general diluent.




  • RMS-104 Sodium Phosphate Monobasic, Monohydrate
  • RMS-105 Sodium Phosphate Dibasic, Anhydrous
  • RMS-106 Sodium Chloride
  • RMS-108 Thimerosal


  • Appropriately sized clean container
  • Stir plate and stir bar
  • Weigh Boats
  • Balance
  • pH Meter
  • pH Standards ( pH 4 and pH 7)
  • Appropriately sized graduated cylinder



  1. Per liter of 25X PBS to be made, measure the following:
         - 6.5 g Sodium Phosphate Monobasic, monohydrate
         - 28.75 g Sodium Phosphate Dibasic, anhydrous
         - 225 g Sodium Chloride
         - 0.1 g Thimerosal
  2. Place the measured components into a container appropriate for the batch size.
  3. Per liter of 25X PBS to be made, add 950 ml deionized water to the container.
  4. Add a stir bar, place container on stir plate and stir for approximately four hours at room temperature until all solids are dissolved.
  5. Standardize pH meter at pH 4 and pH 7.
  6. Measure pH of 25X PBS while stirring. pH should be pH 5.9 - 6.2.
  7. Place in closed container and label with contents and batch number (date).
  8. Store at room temperature up to one year.