Question

As the concentration of an analyte increases, the fluorescent intensity can go through a maximum vs. concentration and then decrease with concentration. Explain this phenomenon.

Answer 1

Answer: In the technique of fluorimetry, fluorescence intensity is dependent on concentration. Ideally, as concentration increases the fluorescence increases. But if the concentration of analyte (showing fluorescence) is very high then in that case after acertain concentration the fluorescence intensity decreases due to quenching effect (self quenching). During quenching phenomenon, the emission by analyte is reabsorbed by the unexcited electron of the molecule and it moves from ground to excited state, and later on emits radiation. Thus there is an internal circulation of the emission radiation and so a false reading is obtained that concentration is low as upon detector less radiation falls.