Objectives=

• Make stock solutions of sodium phosphate, 4-aminoantipyrine, H₂O₂, and horseradish peroxidase.
• Perform an assay on the enzymatic rate of horseradish peroxidase.

0.2 M Sodium Phosphate Buffer in H₂O

• Calculations:
  • 250 mL of 0.2 M sodium phosphate stock solution requires the following:

  MW sodium phosphate: 163.94 g/mol
  Mass sodium phosphate:
        250 mL × (10-3 L/mL) × 0.2 M × (10-3 mol/mmol) × 163.94 g/mol = 13.4035 g sodium phosphate
  Actual mass sodium phosphate: 13.4031 g
  Actual concentration: 
        13.4031 g × (1 mol/163.94 g) × (1/0.25 L) = 0.327 M in H2O

• 13.4031 g of sodium phosphate was dissolved in about 200 mL of H₂O.
• The pH was adjusted to 7.00 by adding 20 mL of 1 N HCl dropwise.
• The solution was then diluted to a final volume of 250 mL with additional H₂O.

Spectrophotometric Analysis of Horseradish Peroxidase Enzyme Activity Rate at 510 nm

• Final concentrations of stock solutions in total volume of 1.5 mL:

• The concentration of H₂O₂ was varied by serial dilution as follows, while the concentrations of all other solutions were kept constant:
  • 8.5 μM, 4.25 μM, 2.125 μM, 1.0625 μM.