Question

Calculate the concentration of protein (g in 8 fluid ounces) in the undiluted nonfat milk for the Biuret and Bradford method and determine the % error of your determinations, using the value reported by the USDA as a reference value (8.45 g of protein in 8 fluid ounces)

Biuret concentration of protein is 3.968 mg/mL

Bradford concentration of protein is 25.902 mg/mL

Please help. thank you!!

Answer 1

We know that 1 g = 1000 mg and 1 ounce = 29.5735 mL; therefore, 8 fluid ounce = (8*29.5735) mL = 236.588 mL.

Biuret concentration of protein = 3.968 mg/1 mL = [(3.968 mg)*(1 g/1000 mg)]]/(1 mL) = 0.003968 g/mL = 0.003968 g/[(1 mL)*(8 fluid ounce/236.588 mL)] = (0.003968 g)*(236.588)/(8 fluid ounce) = 0.93878 g/8 fluid ounce ≈ 0.94 g/8 fluid ounce (ans).

Bradford concentration of protein = 25.902 mg/mL = (25.902 mg)*(1 g/1000 mg)/1 mL = 0.025902 g/mL = 0.025902 g/[(1 mL)*(8 fluid ounce/236.588 mL)] = (0.025902 g)*(236.588)/(8 fluid ounce) = 6.1281 g/8 fluid ounce ≈ 6.13 g/8 fluid ounce.

I believe the reference value for Bradford concentration is 8.45 g/8 fluid ounce; I am not sure if it’s the same for Biuret concentration (please clarify).

Percent error for Bradford concentration = (accepted value – experimental value)/(accepted value)*100 = (8.45 – 6.13)/(8.45)*100 = 27.4556% ≈ 27.45% (ans).