System design of kinetic differentiation mode capillary electrophoresis for separation and determination of ultratrace metal chelates

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A kinetic differentiation (KD) mode determination system for ultra-trace metal ions consists of the derivatization of metal ions by a spectrophotometric reagent followed by separation and detection of the resulting complexes and the free reagent, which has two attractive feature. The first is high selectivity based on the differentiation of the kinetic stability of metal complexes during separation process. The second is high sensitive detection of the complexes owing to the absence of background absorption. The recent advent of capillary electrophoresis (CE) prompted us to transfer the principle of KD to CE in onto to construct new separation/detection systems for metal ions at the fmol level. For instance, 4-(2-pyridylazo)resorcinol was best separated by the simple CE mode, owing to the 1-OH group of the complex having different pKa values among the center metal ions. By using 2,2′-dihydroxyazobenzene-5, 5′-disulfonate (DHABS) and quaternary ammonium ions, ion-association CE was constructed, in which the difference in the ability of ion-association arising from the center metal ion via the -SO3- group determines the separation selectivity. As a result, the requirements for chemical systems in KD-CE were obtained: i) The ligand should possess functional group which is able to convert the character of the center metal ion by means of the reactivity or degree of interaction at the second coordination sphere. ii) An electrophoretic buffer should contain an interacting reagent which can interact with the function group. This guideline successfully produces a new separation system based on the hydrogen-bonding ability of DHABS complexes and poly(ethylene glycohol) through solvated water molecules. Similarly to KD-HPLC, KD-CE exhibited detection selectivity based on kinetic stability of metal complexes. Taking advantage of the simplicity of the separation processes of KD-CE, a CE reactor was constructed to measure the solvolytic dissociation rate of metal complexes which determines the kinetic selectivity in KD mode systems.

Original languageEnglish
Pages (from-to)495-505
Number of pages11
JournalBunseki Kagaku
Issue number7
Publication statusPublished - 2002 Jul


  • CE
  • Dissociation reaction
  • HPLC
  • Kinetic differentiation
  • Metal chelates


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