An unknown sample of dopamine gave a current of 34.6 nA in the electrochemical analysis. Then 2.00 mL of a solution containing 0.015 6 M dopamine was mixed with 90.0 mL of the unknown, and the mixture was diluted to 100.0 mL in a volumetric flask. The signal from the new solution was 58.4 nA.

(a) Denoting the initial, unknown concentration as [dopamine]i, write an expression for the final concentration, [dopamine]f, after dilution.

(b) In a similar manner, write the final concentration of added standard dopamine, designated as [S]f.