Excess Absorbance as a Novel Approach for Studying the Self-Aggregation of Vital Dyes in Liquid Solution

Abstract

In the present paper, a simple method for analyzing the self-aggregation of dyes in a solution by a UV-visible absorption measurements is proposed. The concept of excess absorbance is introduced to determine an equation whose coefficients determine the parameters of the aggregation equilibrium. The computational peculiarities of the model are first discussed theoretically and then applied to sodium fluorescein in polar protic and aprotic solvents, as well as in aqueous solutions of methylene blue, which is a cationic dye. Although the experimental responses are very different, the model appears to work equally well in both cases. The model reveals that the trimer is the most likely configuration in both solvents. Furthermore, aggregation is strongly favored for the protic solvent. Interestingly, the model establishes that in aqueous solutions of methylene blue, the tetramer is the predominant form, which has long been assumed and recently demonstrated with sophisticated computational techniques.

A Novel Approach to Optimize the Industrial Process of Membrane Concentration of Grape Musts

“…Results collected in Tables 4 and 5 show how sugar content, dry extract, and alcohol potential reach commercially optimal values in both reverse osmosis and nanofiltration processes when the membranes operate under higher pressure, i.e., 60-70 bar for RO membranes and 30-40 bar for NF membranes. Since the selected membranes exhibited a complete block fouling mechanism during laboratory tests, Equation (20) was used to estimate the sugar concentration in the tank. The correlation plot of Figure 5, where C P calculated by Equation ( 20) is plotted versus experimental C P , is linear with R 2 = 0.90.…”

“…In order to establish the filtration mode, experimental values were fitted to Equation (8) for n = 0, 1, 1.5, and 2. Using the Levenberg-Marquardt nonlinear least squares procedure for each n-value, the root mean squared error (RMSE) of the observed compared to the predict was computed [20]. The n-value corresponding to the smallest RMSE is considered to be the filtration mode.…”

Kinetic Model of Fluorescein Release through Bioprinted Polylactic Acid Membrane

“…It is immediately clear that at higher concentrations the linearity of the calibration curve is lost. This effect is due to the dye–dye association equilibria which take place in aqueous solutions and are explained elsewhere [ 26 , 36 , 37 ]. Each point used to construct the calibration curves is the average of triplicate measurements.…”