A Capillary Electrophoretic Reactor with an Electroosmosis Control Method for Measurement of Dissociation Kinetics of Metal Complexes

Abstract

The solvolytic dissociation rate constants of 1:2 complexes of Al3+ and Ga3+ with an azo dye ligand, 2,2'-dihydroxyazobenzene-5,5'-disulfonate (DHABS, H2L2-), have been evaluated with a capillary electrophoretic reactor (CER) system. This CER system is based on the fact that metal complexes encounter an overwhelming force to dissociate when apart from the ligand by CE resolution. Treatment of a capillary with a slightly acidic buffer solution, e.g., pH 5, reduces the double-layer potential (zeta) of the inner silica wall. Owing to slow relaxation of the deprotonation equilibria of superficial silanol groups known as the pH hysteresis, this zeta potential can be actually retained during the electrophoresis of the metal complexes in question with a neutral buffer at pH 7.0. This method enables one to manipulate migration times, namely, residence times in a capillary tube, from 5 to 90 min, depending on the prescribed conditioning pH, without changing any other operation conditions such as buffer composition and electric field strength. The excellent performance of the CER is exemplified by the accurate estimation of the dissociation degree of the complexes. The dissociation degree-time profiles for the complexes are quantitatively described using both internal and external standards; the very inert complex of [Co(III)L2]5- for the peak signal standardization and methyl orange for the injection volume correction. The solvolytic dissociation rate constants of the 1:2 complexes of Al3+ and Ga3+ ions with DHABS [AlL2]5- and [GaL2]5- into the 1:1 ones have been determined as (4.9+/-1.0) x 10(-4) and (3.7+/-0.3) x 10(-3) s(-1) at 303 K, respectively.

Dissociation Kinetic Analysis of Ce(III) Complex with Quin2 by Microchip Capillary Electrophoretic Reactor

“…For the kinetic analysis of [Ce III L], the peak height signals were employed because the peak area data may give unreliable results caused by asymmetric peak profiles owing to products of dissociation reaction, such as free Quin2. 3 Because solvolytic dissociation reaction follows the first-order kinetics, the rate law is given by,…”

“…[3][4][5] The basic concept of CER is using the capillary electrophoretic separation process as the reactor for the dissociation reaction of the metal complexes.…”

Analysis of Ion-Association Reaction in Aqueous Solution and Its Utilization by Capillary Zone Electrophoresis

“…108 Solvolytic dissociation rates of metal-DHABS complexes were evaluated by capillary electrophoretic reactor by controlling the migration time of the complex to detector. 109 Relative peak height was used for the rate analysis, and the rate constants for Al and Ga complexes were determined. Nonequilibrium capillary electrophoresis is also proposed for revealing equilibrium and kinetic parameters of protein-DNA interactions.…”

MEMS Microfluidics for Lab-on-a-Chip Applications

“…Electroosmotic micropumps have been used widely in broad applications [33,34]. Novel micropumps based on ACEO have been designed to drive fluids.…”