Sodium phosphate buffer (0.2 M)

MATERIALS

METHOD

• 1. Dissolve 35.61 g of Na₂HPO₄•2H₂O and 27.6 g of NaH₂PO₄•H₂O separately in H₂O.

• 2. Adjust the volume of each solution to 1000 mL.

  Store the stock solutions for up to 6 mo at 4°C.

• 3. To prepare the buffer, mix the stock solutions as follows:

  • i. For 50 mL: 38.5 mL of Na₂HPO₄•2H₂O and 11.5 mL of NaH₂PO₄•H₂O.

  • ii. For 100 mL: 77 mL of Na₂HPO₄•2H₂O and 23 mL of NaH₂PO₄•H₂O.

  • iii. For 500 mL: 385 mL of Na₂HPO₄•2H₂O and 115 mL of NaH₂PO₄•H₂O.

  • iv. For 1000 mL: 770 mL of Na₂HPO₄•2H₂O and 230 mL of NaH₂PO₄•H₂O.

• 4. Check the pH of the solution at room temperature. If necessary, adjust the pH to 7.3.