141. Solving a chemistry problem

5. In 0.1 M KCI (pH7), D-riboflavin C17H20N4O6, thiamine C12H17N4OSCl.HCl and nicotinic acid C5H4NCOOH have half-wave potentials E1 / 2, respectively: –0.35; -1.25;
- 1.17 V. To construct the calibration curves, polarograms of four standard solutions of these substances with a concentration of 0.000400 were recorded; 0.000600; 0.000800 and 0.001000 mol / L and measured the strength of the diffusion current Id under the appropriate conditions (–0.6; –1.5; –1.8 B):
Standard substance Id, mkA
D-Riboflavin 2.40 3.60 4.80 6.00
Thiamine 3.60 5.40 7.20 9.00
Nicotinic acid 2.20 3.30 4 40 5.50

Calculate the concentrations (mg / ml) of D-riboflavin, thiamine and nicotinic acid in the analyzed solution, if the obtained polarogram had three waves at the corresponding potentials and the diffusion currents Id were equal:
Substance le, μA for variants
1
D-Riboflavin 2.80
Thiamine 7.50
Nicotinic acid 4.10