Disclosed is a method of monitoring and optimizing the concentration of an additive composition in a fuel ethanol. The method includes adding a known amount of the additive composition to the fuel ethanol to create a treated fuel ethanol. A measured fluorescent signal provides information for determining the concentration of the additive composition in the fuel ethanol. A component in the additive composition is capable of providing the fluorescent signal or capable of being chemically derivatized to provide a fluorescent signal or a calorimetric signal. Based upon the measured fluorescent signal or calorimetric signal, the concentration of the additive composition in the fuel ethanol may be adjusted.