Question

Back calculate the amount of riboflavin in your sample from the concentration you calculated, assuming you took 7.5% of a whole tablet into 200 mL of acetate buffer, and then diluted 1.0 mL of that solution to 250 mL (the same procedure you used from the lab). Show your work. Concentration calculated is 51.5ng/ml.

Answer 1

The concentration of Riboflavin in the diluted solution is 51.5 ng/mL. We took 1.0 mL of the prepared sample solution and diluted to 250.0 mL so that the dilution factor is (250.0 mL)/(1.0 mL) = 250.0.

Therefore, concentration of Riboflavin in the prepared sample solution is (51.5 ng/mL)*(dilution factor) = (51.5 ng/mL)*(250.0) = 12875.0 ng/mL.

We prepared 200.0 mL of the acetate buffer solution and dissolved the tablet in the actate buffer; therefore, mass of Riboflavin dissolved = (12875.0 ng/mL)*(200.0 mL) = 2575000 ng = (2575000 ng)*(1 g/1.0*10⁹ ng) = 0.002575 g.

As per the problem, 0.002575 g of Riboflavin is present in 7.5% of a whole tablet; therefore, mass of Riboflavin present in the whole table (100%) is (0.002575 g)*(100%/7.5%) = 0.03433 g = (0.03433 g)*(1000 mg/1 g) = 34.33 mg (ans).