Equilibrium Analysis of Reactions of Metal-Pyridylazoresorcinolato Chelates with Quaternary Ammonium Ion, Nonionic Surfactant and Polyethylene Glycol in Aqueous Solution by Capillary Zone Electrophoresis

Abstract

Capillary zone electrophoresis (CZE) is a powerful tool for the separation and determination of ionic substances. Metal ions have been determined after derivatizing them with chelating reagents to convert anionic complexes. Ethylenediaminetetraacetic acid 1 and 8-quinolinol-5-sulfonic acid 2 were utilized as derivatizing reagents for the determination of alkaline earth metals by CZE analysis. Some pyridylazo compounds were also used for the derivatization and determination of transition metal ions. [3][4][5] 4-(2-Pyridylazo)resorcinol (par) has been used as a spectrophotometric reagent and a metallochromic indicator for metal determination, and equilibrium reactions of chelate formation have been investigated in aqueous solutions, as well as in liquid-liquid distribution systems, including ion-pair extraction. [6][7][8][9][10] The properties of the chelates were utilized for the separation of heavy metal ions by ion-pair reversed-phase high performance liquid chromatography, 11,12 and also for CZE separations. [13][14][15][16] Recently, sodium dodecyl sulfate has been used in micellar electrokinetic chromatography (MEKC), and in the separation of the par chelates in MEKC. 17 Cationic polymers have also been used as an interacting reagent for anionic chelates. 18 In the capillary electrophoretic separation of the par chelates, it was reported that some metal chelates decomposed during migration. 13,17 The hydroxyl groups of the par chelates have been reported to dissociate in aqueous solutions. However, such interesting properties as acid dissociations, interactions with cations and surfactants, and their equilibrium reactions in aqueous solutions have not yet been clarified, because of the lack of an analysis method. The electrophoretic mobility of ions can provide useful information on the dissolved states of analytes, and equilibrium constants can be determined by analyzing the mobility change. In this study, the authors investigated several properties of the par chelates, including acid dissociation, ion association with quaternary ammonium ions, as well as binding reactions to nonionic surfactant micelle and polyethylene glycol. The utilization of CZE measurements has major advantages in that the analyte concentrations can be lowered to the 10 -5 M level or less, 19 and that the migration time of the species of interest can be used even when they gradually decompose during migration. 20 Experimental ApparatusA Hewlett Packard 3D CE was used as a capillary electrophoresis system. A fused-silica capillary (Hewlett Packard) was attached to the system; the dimensions of the capillary were 56.5 cm in total length, 50 cm in effective length from the injection point to the detector, and 50 µm inner diameter. The resolutions of metal-4-(2-pyridylazo)resorcinol chelates by capillary zone electrophoresis (CZE) were investigated in the presence of some interacting reagents; also, equilibrium reactions between the chelates and the interacting reagents were analyzed in an aqueous solution. Among nine metal chelates forme...

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

“…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].…”

“…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.…”

“…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.…”

Capillary electrophoresis of inorganic ions: An update

“…Electrophoretic mobility measurements using CE enable the direct equilibrium analysis of weak ionic interactions [263] such as complex formation between alkali and alkali earth metal ions and crown ethers [264,265], including macrocyclic substituents of metal chelates [212], or ion association between inorganic anions [63], or metal-PAR complexes [266] and tetraalkylammonium ions. In the latter contribution, the acid-dissociation constants of anionic chelates and their binding constants with a nonionic surfactant (Brij 35) and polyethylene glycol were also determined.…”

<b>Use of weak ion association in the separation of inorganic anions by capillary electrophoresis with specific application to simultaneous-trace determination of bromate and iodate in drinking water</b>

“…However, for the separation of inorganic anions, significant changes in selectivity can be achieved by ion association or addition of an organic solvent to the migrating buffer/ electrolyte or a combination of the two strategies. Studies on strong ion association between quaternary ammonium and aromatic ions [15]; metal ions with crown ethers and metalpyridylazoresorcinolato with quaternary ammonium ions [16], nonionic surfactants and polyethylene glycol [17] have already been reported. Compared to strong ion association, weak ion association, which involves interaction between tetraalkylammonium ammonium ions and small inorganic anions has received less attention.…”