Spectrophotometric analysis of sodium fluorescein aqueous solutions. Determination of molar absorption coefficient.

The usefulness of sodium fluorescein (SF) and related physical parameters were analysed. Two factors that may affect the molar absorption coefficient (epsilon) of this compound were the presence of impurities and the pH of the solution. As discrepant values can be found in the literature for that coefficient, a purification technique was used and SF quantification was performed according to sodium concentration determined by atomic absorption spectrophotometry. The molar absorption coefficient of the SF solution in phosphate buffer pH 7.4 was determined. To study the influence of pH on epsilon determination, absorption spectra at pH1, 3, 5, and 10 were also analysed.