Ion-selective microelectrodes were prepared by coating a matrix containing the crown ether benzo-18-crown-6 or one of five polyether ring-substituted benzo-18-crown-6 derivatives on a preconditioned silver wire in a flow cell. Responses of the electrodes toward lithium, sodium, potassium, magnesium, calciuni, strontium, and lead were measured. Selectivity coefficients were obtained by the matched potential, fixed interference, and separate solution methods. Compared with benzo-18-crown-6, the nature of the side arm in the lariat ether derivatives was found to influence the selectivities in different ways. For specific ionophores, high selectivities of potassium over lithium, sodium, magnesium, calcium, and strontium, of strontium over magnesium and calcium, and of lead over magnesium, calcium, and strontium were demonstrated.
E&ptI~qxwtment of Chmiistr)l, 1%-10, llnirlersit?, of Wasbington, Seattle, Wasbington 981 95, USA ABSTRACT Seven comix)iiiids o f a new class o f ionopliores, acyclic nionoxadianiides, were synthesized and tested for the potentiometric selectivity for lithium ion, i n polyvinyl chloride ( WC) membrane electrodes. Four different plasticizers were studied: o-nitroplienyloctyl ether (NPOE), o-nitrophenylphenyl ether (NPI'E), o-nitroplienylbutyl ether (NPHE), and o-nitrophenylbenzyl ether (NI'HnE), as was the addition of trioctylphospliine oxide (TOPO). The ionophore 0-carboxyphenoxyacetic acid dimorpholide (Ig) exhilJited sodiuni-lithium selectivity, IV~',','~.~, o f 0.018 by the matched-potential method in the presence of 1% T01'0 using NI'HE plasticizer. The presence o f TOPO generally causes a substantial increase in the lithium selectivity, but it decreases the slopes o f the calibration curves. Selectivities are reported for sodium, potassium, ammonium, barium, and calcium ions with respect t o tlie lithium ion.
Five crown ethers with four ring oxygen atoms and different types of pendant groups were used t o prepare ion-selective electrodes by coating a membrane containing the crown ether on the tip o f a silver wire incorporated in a flow cell. A flow injection analysis study was conducted to determine the potentiometric selectivities of the crown ethers for lithium, sodium, potassium, magnesium, and calcium ions. It was found that crown ethers with neutral side arms show selectivities for lithium over other ions, while those of acidic side arms show selectivities for potassium over the other ions. The effect of the addition of trioctylphosphine oxide to the electrode matrix was also investigated. A comparison is made between the potentiometric selectivities of the crown ethers for certain metal ions and tlieir selectivities in extracting the ions into an organic phase.
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