title: Semi-empirical spectrophotometric (SESp) method for the indirect determination of the ratio of cationic micellar binding constants of counterions X⁻ and Br⁻(K(X)/K(Br)).
abstract: The semi-empirical spectrophotometric (SESp) method, for the indirect determination of ion exchange constants (K(X)(Br)) of ion exchange processes occurring between counterions (X⁻ and Br⁻) at the cationic micellar surface, is described in this article. The method uses an anionic spectrophotometric probe molecule, N-(2-methoxyphenyl)phthalamate ion (1⁻), which measures the effects of varying concentrations of inert inorganic or organic salt (Na(v)X, v = 1, 2) on absorbance, (A(ob)) at 310 nm, of samples containing constant concentrations of 1⁻, NaOH and cationic micelles. The observed data fit satisfactorily to an empirical equation which gives the values of two empirical constants. These empirical constants lead to the determination of K(X)(Br) (= K(X)/K(Br) with K(X) and K(Br) representing cationic micellar binding constants of counterions X and Br⁻). This method gives values of K(X)(Br) for both moderately hydrophobic and hydrophilic X⁻. The values of K(X)(Br), obtained by using this method, are comparable with the corresponding values of K(X)(Br), obtained by the use of semi-empirical kinetic (SEK) method, for different moderately hydrophobic X. The values of K(X)(Br) for X = Cl⁻ and 2,6-Cl₂C6H₃CO₂⁻, obtained by the use of SESp and SEK methods, are similar to those obtained by the use of other different conventional methods.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia. niyaz@um.edu.my
authors.forename: Mohammad Niyaz
authors.initials: MN
authors.lastname: Khan
authors.forename: Nor Saadah Mohd
authors.initials: NS
authors.lastname: Yusof
authors.forename: Norazizah Abdul
authors.initials: NA
authors.lastname: Razak
mesh_terms: D002412:Cations; D055598:Chemical Phenomena; D057927:Hydrophobic and Hydrophilic Interactions; D007474:Ion Exchange; D008823:Micelles; D013053:Spectrophotometry / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water
chemical_list: D002412:Cations; D008823:Micelles; D013501:Surface-Active Agents; D014867:Water