The present invention relates to a method for compensating for the breakdown of a reagent stored in an aqueous phase comprising at least one fluorescent compound and enabling the identification of particles, including the steps of: (i) measuring the fluorescence level FLUOm(t) of particles marked with said reagent; (ii) measuring the absorbance at at least one wavelength of a solution of said reagent, at a time t close to the time of said fluorescence level FLUOm(t) measurements, so as to determine at least one current optical density DO(t) of the reagent; and (iii) calculating a correction of the fluorescent level measurements using said at least one current optical density DO(t) and at least one initial optical density DO(0) of the reagent that has not been broken down. The invention also relates to a biological analysis device implementing the method.