3. Results and discussion
Diclofenac is soluble in water and emits fluorescence
at 36292 nm when excited at 28793 nm
(Fig. 1). The spectral characteristics are almost
independent of the solution pH. However, significant
changes of the fluorescence intensity as a
function of pH were observed (Fig. 1). The plot of
fluorescence intensity as a function of pH is a
sigmoid with an inflection point near pH approximately
3, as expected from the equilibrium between
the protonated and deprotonated forms of
diclofenac. This previous study indicated that
suitable conditions for the analytical determination
of diclofenac involve maintaining the pH in
the range 1–2.