surement conditions using the same plasticizer in all membranes. In addition, comparison is made with a 14-crown-4 ether neutral carrier as reported by Kitazawa et al. (5).Cation complexing properties of a large number of macrocyclic polyether-diester compounds have also been reported (6-19). These compounds generally form weaker complexes than the cyclic polyethers. They have been reported to show significant affinities for alkali, alkaline-earth, and primary alkylammonium cations (12,13,15,16,19). Gadzekpo et al. have reviewed the literature of lithium sensors (20). EXPERIMENTAL SECTION Reagents and Chemicals. High molecular weight poly(vinyl chloride) (PVC) was obtained from Fluka AG. Tris(2-ethylhexyl) phosphate was obtained by U. C. C. Flexoh. All solutions were
Lithium km selective electrodes Incorporating the 14-crown-4 ether 3-dodecyl-3-methyH ,5,8,12-tetraoxacyclotetradecane In PVC membranes were constructed In a microconduit circuit, by deposition on platinum, silver, or copper wires. A^J,
Trioctylphosphine oxide (TOPO) acts as a neutral lithium carrier in lithium ion-selective electrode membranes. When TOPO was used with 1% potassium tetrakis(pchloropheny1) borate in NPOE -PVC membranes, the electrodes exhibited a nearly Nernstian response and had a lithium to sodium selectivity of 1 : 60, which is better than some electrode sensors reported earlier. TOPO was also added to 14-crown-4, ETH 1810 and UWXC 10 electrode membranes, and the lithium to sodium selectivity of the 14-crown-4 electrode was dramatically improved. However, TOPO had a negative effect on the selectivities of the ETH 1810 and UWXC 10 electrodes. Diluted serum samples were analysed for lithium using the 14-crown-4 -TOP0 electrode in an FIA system. A statistical analysis of the ISE and corresponding AAS results indicated that these two methods have no statistical difference at the 95% confidence level. Because of the improved selectivity of the electrode and the elimination of the dialysis membrane from our original FIA design, the precision and accuracy of this determination were both improved, and the measurement time decreased.
Measurements were made of selectivity coefficients for lithium ion-selective electrodes containing five different lipophilic diamide ionophores with combinations of three different backbones and three different sidechains, in PVC membranes containing pNPOE plasticizer. Comparing with results for similar membranes containing tris(2-ethylhexy1)phosphate plasticizer revealed that use of pNPOE plasticizer enhances the selectivity for lithium with respect to sodium only for ionophores with the -N+T sidechain, irrespective of the backbone.
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