Separation of Divalent Aromatic Anions by Capillary Zone Electrophoresis Using Multipoint Ion Association With Divalent Quaternary Ammonium Ions

Abstract

Positional isomers of naphthalenedisulfonate (NDS), naphthalenedicarboxylate (NDC) and phthalate were separated using an ion association reaction in aqueous solution followed by capillary zone electrophoresis with a polymer coated capillary. By using divalent quaternary ammonium ions, four NDS isomers and three NDC isomers were completely resolved, although some of the isomers were not resolved with tetrabutylammonium ion. Ion association constants, K ass , between the anions and the divalent quaternary ammonium cations were also determined by analyzing the change in electrophoretic mobility using a non-linear least-squares method. The K ass values of the anions obtained with the divalent cations were larger than those with tetrabutylammonium ion because of an increased electrostatic interaction. The ion associability was also explained on the basis of a distance-fitting concept and the hydrophobicity concept of the pairing cations. Ion associability was also improved by using a better distance-fitting pairing ion. From the results obtained, it was suggested that the charge-charge distance in cationic and anionic molecules must be close, and the charge-charge distance of the divalent cations was about 0.2 nm longer than that of divalent anions for good ion associability (a distance-fitting concept).

Evaluation of weak ion association between tetraalkylammonium ions and inorganic anions in aqueous solutions by capillary zone electrophoresis

“…The aim of this work therefore, was to determine association constants, K ass between the small inorganic anions and tetraalkylammonium ions in aqueous media at 25 • C, by measuring of the mobility of anions using a coated capillary. This work reports on the aforementioned weak ion association with a view of assessing the method, based on related works [14][15][16][17][18][19][20][21] and discusses the observed trends in association constants, K ass and mobility of the inorganic anions.…”

“…As a result CZE is capable of studying the interactions in organic as well as aqueous media, where small changes in mobility often occur due to limited association. Studies on strong ion-ion interactions by CZE, involving quaternary ammonium with aromatic ions [14][15][16][17][18]; metal ions with crown ethers [19,20] and metal-pyridylazoresorcinolato chelates with quaternary ammonium ions, non-ionic surfactants and polyethylene glycol [21] have been previously reported. The stated interactions were investigated with the use of ordinary silica capillary by monitoring the mobility of bulky ions, which often possess low mobility and display strong interactions with the pairing ion.…”

“…Another important feature of early ion-ion conductometric study was that most of the measurements were made in organic solvents because of the ease with which equilibrium constant could be determined. Alternatively, the same interactions can be investigated by capillary zone electrophoresis [13][14][15][16][17][18][19][20][21] which offers benefits like multi-ion, low ion concentration analysis and precise control of experimental conditions such as ionic strength, pH, etc. [14].…”

Separation of positional isomers of aromatic anions by capillary electrophoresis using quaternized porphyrazine ion in aqueous solution

“…Maichel et al [5] used PEI for the separation of uncharged phenols and proposed that ion-dipole interaction between 1OH groups of phenolic isomers and PEI is responsible for separation. Takayanagi et al [6,7] separated positional isomers of aromatic anions using the ion association reaction between the anions and quaternary ammonium ions in aqueous solution. They suggested that ion association was governed by hydrophobicity of the pairing cation.…”

Analysis of Binding Equilibrium of Phenylalkylamines to Brij 58 Micelle through the Measurement of Electrophoretic Mobility by CZE

“…Acidity constants in 50% methanol/water [10] and in 100% methanol [11] were determined. Changes in electrophoretic mobility of analytes were also utilized to investigate the chemical equilibria of complex formation [2], ion-association [2,[12][13], and inclusion to cyclodextrins [14][15][16].…”