Catalase performic acid reaction

Units of catalase, into a 200-mL beaker. Rapidly add 100 mL of Peroxide Substrate Solution, previously adjusted to 25°, and stir immediately for 5 to 10 s. Cover the beaker, and incubate at 25° 1° until the reaction is completed. Stir vigorously for 5 s, and then pipet 4.0 mL from the beaker into a 50-mL Erlenmeyer flask. Add 5 mL of 2 N sulfuric acid to the flask, mix, then add 5.0 mL of 40% potassium iodide solution, freshly prepared, and 1 drop of Ammonium Molybdate Solution (1%), and mix. While continuing to mix, titrate rapidly to a colorless endpoint with 0.250 N Sodium Thiosulfate, recording the volume, in milliliters, required as S. Perform a blank determination with 4.0 mL of Peroxide Substrate Solution, and record the volume required, in milliliters, as B. 

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