Spectrophotometric characteristics and assay of pure pyronin Y
SummaryThe spectrophotometric characteristics of analytically pure pyronin Y have been investigated. Addition of metal ions (Fe3+, Zn2+, and Mg2+) and of dextrin were shown not to influence the absorption characteristics. The composition of the solvent strongly influenced the value of the extinction coefficient. Aqueous ethanolic solutions with a content of about 50% ethanol gave higher ε-values than those found for more concentrated ethanol solutions. The difference can be explained by the existence of a solvent-solute complex in the less concentrated ethanol solutions. A new spectrophotometric assay is proposed using the ε-value 11.7×104 lmol−1 cm−1 found in aqueous ethanol (52%) as standard.
Some Spectral Studies of the Aqueous Solution of Pyronine G
Th effect of inorganic anions on the dimerization constant of pyronine G in an aqueous solution was examined. It was found that the effect is very specific and can not be explained simply by the effect of the ionic strength. The analysis led to the conclusion that a dimer exists as an ion-pair with the anions attached laterally to dye ions instead of being sandwiched between two dye ions. The change of absorption spectra in the alkaline solution was interpreted to be due to the formation of carbinol, and from its analysis the formation constant of carbinol was determined. Carbinol was found to have also its proper fluorescence, and from the pH change of fluorescence spectra the formation constant of carbinol was again decided, the value of which coincided well with that obtained from the absorption spectra.
Note on the Polymerization of Dyes in Solution
The effect of concentration on the absorption spectra of DAA and BDAA in various organic solvents was studied in the concentration range from 10−6 to 10−2mol./l. Contrary to Levshin’s opinion, DAA forms polymers higher than dimer very easily in some organic solvents, and the association tendency of DAA is greater than that of BDAA. Further, the association of these molecules is very sensitive to the solvents used. The association tendency and the spectral shift due to dimerization or polymerization have no correlation with the oscillator strengths of monomeric bands of these molecules, and this is true also for the various dye ions in aqueous solution.