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Flow-through type fiber-optic chloride ion selective optodes have been developed based on chloride adducts of lipophilic organometallic compounds, including a metal: Sn, Ge, Hg or Hf and a lipophilic anionic indicator dye of the Biphenyl amine type. The pellicular-type ODS beads were coated with a lipophilic organic liquid containing the lipophilic organometallic compound as the anion-selective ionophore ligand and LAD-3 as the color changeable indicator dye. The optode system was constructed by packing these color changeable ion sensing beads in the flow-through optical cell (cell volume, 7 µl) having a quartz window attached directly to the distal end of a bifurcated optical fiber . The optode based on tricyclohexyltin chloride (TCTCI) exhibited the most sensitive response to chloride ion among all the sensors using the organometallic compounds investigated. This optode could detect chloride ion in the concentration ranging from 10.4 to l M at pH 6.5 with a 0.01 M sodium phosphate buffer as the flowing solution by measuring the absorbance change in the sensing beads at 516 nm. This optode showed sufficient selectivity for the determination of chloride ion in normal human serum. Several types of optical ion sensors (ion-selective opt(r)odes) based on various neutral ionophores have recently been developed.l-9 Some of these optodes utilize lipophilic ionic indicator dyes which act as counter-ions when neutral ionophores form complexes with the respective analyte ions.2-9 The advantages of these types of optodes have been discussed in detail in recent reviews. 10-12 Not only are these electrodes similar to these ion-selective electrodes (ISEs), but they also have the possibility of higher sensitivity and selectivity compared to these ISEs, in the case where the same ionophore is used for the sensing material.2 In contrast to the cation-selective ionophores, novel anion-selective ionophores (except the classical anion exchangers of quaternary ammonium salts6'8) have been only slightly investigated: the metalloporphyrin derivatives 13,14 macrocyclic polyamine15, and lipophilic organometallic compounds.9,16 Among them, some of the organometals of the cobalt and tin complexes have been used for the ion-sensing materials of the ISE. They show unusual selectivity patterns, different from the so-called Hofmeister sequence that is usually obtained in the case where a classical anion exchanger such as a tetraalkylt To whom correspondence should be addressed .ammonium chloride is used for the anion sensing material for the ISE. Unfortunately, however, most of the electrodes based on these organometal complexes have negative properties for practical use: e.g. slow response, poor reproducibility, etc. Therefore, the electrodes based on a classical anion exchanger of the quaternary ammonium ion type such as the tetraalkylammonium ion have usually been used in the practical measurements of anions in clinical analysis (for chloride ion) and environmental sample measurements, even though the electrode is simply obeying the Hofme...

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