Ashraful Islam .... Unless there is an equilibrium of the starting compound with a protonated species, there will be no influence of the added salts on the fluorescence excitation... Good luck

Hi, Ashraful Islam, if you talk about NaOH and HCl, i.e., a base and an acid, yes, there may be a dramatic change in excitation and emission spectra of eluted material. It depends on how strongly pH is changed. The reason for possible spectral changes is ionization of molecules. Ionized phenols or aromatic acids may have different excitation emission spectra as compared with their molecular forms. Protonated proteinaceous matter (due to the presence of fluorescent aminoacids) may also change the spectra. When different species are at equilibrium, the change of spectra and shifts are possible. If the pH is changed within 1 log unit, most probably fluorescence of humic-like substances does not change, but it is also depends on the specific pH range. Above pH 8, you will have ionization of phenolic moieties. Below pH 5-6, there is protonation of carboxylic groups. So, if pH is the question, due to the use of bases or acids for elutions and pH adjustment, their role has to be considered explicitly and verified. If finally, you mean indeed the role of salts, their effect might be much less (albeit, it seems to me less documented).