Lithium ion-selective electrodes containing TOPO: determination of serum lithium by flow injection analysis

Abstract

Trioctylphosphine oxide (TOPO) acts as a neutral lithium carrier in lithium ion-selective electrode membranes. When TOPO was used with 1% potassium tetrakis(p-chlorophenyl) 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-TOPO 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.