Spectrophotometric and spectrofluorometric pH titrations

Appendix A. Spectrophotometric and spectrofluorometric pH titrations Single-wavelength measurements 

The concentration of the indicator is kept low enough that the linear relationship between aborbance or fluorescence intensity and concentration is fulfilled. 

At a given wavelength, where both acidic form A and basic form B absorb or emit, the absorbance or the fluorescence intensity, denoted Y, are given by 

In spectrophotometry, Y is the absorbance A(X) of the solution at the chosen wavelength L According to the Beer-Lambert law, a and b are the products of the absorption pathlength by the molar absorption coefficients of A and B, respectively. 

In spectrofluorometry, Y is the fluorescence intensity If(Ae,Af) of the solution for a couple of excitation and observation wavelengths, a and h are proportional to the molar absorption coefficients (at the excitation wavelength) and the fluorescence quantum yields of A and B, respectively. 

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