ONE-STEP PARAMETER-ESTIMATION OF THE ACID-BASE EQUILIBRIA IN THE GROUND AND EXCITED-STATES OF 2-NAPHTHOL BY GLOBAL COMPARTMENTAL ANALYSIS OF THE FLUORESCENCE DECAY SURFACE

In this paper a new implementation of global bicompartmental analysis of the fluorescence decay surface is presented and applied to the acid-base equilibria in the ground and excited states of 2-naphthol. It is shown that, when the total concentration and absorbance in the ground state of a bicompartmental system are known, global bicompartmental analysis allows one to fit directly for the rate constants of the excited-state process, the normalized spectral emission weighting factors, the equilibrium constant of the ground-state process and the extinction coefficient of one of the species. This one-step global compartmental analysis yields the following values for the rate constants, the ground-state acidity constant and the extinction coefficient of 2-naphtholate at 320 nm: k01=(1.12+/-0.01)x10(8) s-1, k21=(5+/-1)x10(10) M-1 s-1, k02=(1.33+/-0.01)x10(8) s-1, k12=(7.1+/-0.6)x10(7) s-1, K(a)=(2.7+/-0.4)x10(-10) M and epsilon=1600+/-300 M-1 cm-1.These values are in good agreement with those reported previously from separate analyses of fluorescence and absorbance. The species-associated emission and excitation spectra of the 2-naphthol and 2-naphtholate emission are calculated from the steady-state spectra and the obtained fluorescence decay parameters.