Application of factor analysis to the study of the forms of succinylfluorescein present in buffer solutions in...

The pH-dependent forms adopted by the xanthene dye succinylfluorescein in 1:1 v/v aqueous methanol buffers have been deduced from factor analysis of absorbance data measured at six wavelengths in the visible region, and sixteen pH-values. It is concluded that a protonated species and a doubly-charged anion are the only absorbing species at the two ends of the pH-range studied, 1.40-9.77, and the quinonoid neutral and singly charged anion forms, both with similar absorption properties, are the major components in the pH-range 5-6. A colourless minor compound may also be present at around pH 4. Apparent pK values corresponding to the three ionizations involved are 2.90, 4.60 and 6.80, as determined by potentiometry.