TITLE:
Shift in pKa of 1,10-Phenanthroline in TBAB and PEG-400 Micellar Media: A Potentiometric Study
AUTHORS:
Atnafu Guadie Assefa, Rongali Srinivasu, Pulipaka Shyamala, Gollapalli Nageswara Rao
KEYWORDS:
Protonation Equilibria, 1, 10-Phenanthroline, MINIQUAD75, PEG-400, TBAB Micelles
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.9 No.9,
September
5,
2018
ABSTRACT: The acid-base equilibrium of 1,10-phenanthroline (1,10-phen) in the presence of polyethylene glycol 400 (PEG-400, non-ionic) and tetrabutylammonium bromide (TBAB, ionic) micellar media has been studied by Calvin-Wilson titration technique at different mole fractions (0.5% - 2.5%) of PEG-400 and TBAB micellar solutions at an ionic strength of 0.16 mol dm-3 NaCl and at a temperature of 298 K. The pH metric data were subjected to SCPHD program to obtain correction factor and Kw which were given as initial inputs for MINIQUAD75 program to refine protonation constants. HySS program was then used to generate the species distribution diagrams versus pH using the results obtained from the MINIQUAD75 program and SIM run data. The difference in values of protonation constants in aqueous medium (logβ1 = 4.93 & logβ2 = 6.22) and in the micellar media (PEG-400, logβ1 = 4.89 & logβ2 = 5.91 and TBAB, logβ1 = 4.84 & logβ2 = 5.73) is attributed to different intrinsic solvent characteristics of micelles. In case of ionic surfactants, the electrostatic micellar surface is an additional contributing factor.