LIPOPHILIC CROWN-4 DERIVATIVES AS LITHIUM IONOPHORES FOR LITHIUM ION-SELECTIVE LIQUID MEMBRANE ELECTRODES

New lipophilic Crown-4 compounds of 16-membered rings containing furan (neutral carrier, 1), tetrahydrofuran (neutral carrier, II) and lithium complex of the latter (neutral carrier, III) have been synthesized and tested as the active sensors for lithium ion in poly (vinyl chloride) (PVC) membrane electrode, in the presence and absence of an anion excluder, tetrakis (4-chloro-phenyl) borate (KTClPB). 2-nitrophenyl phenyl ether (NPPE), tris (2-ethylhexyl) phosphate (TEHP), o-nitrophenyl octyl ether (NPOE), dioctyl adipate (DOA), bis (2-ethylhexyl) adipate (BEHA), di-n-octyl phenyl phosphonate (DOPP) were used as plasticizing solvent mediators. The electrode response function had a nearly Nernstian slope of 54-61 mV per decade (25-degrees-C ) within the concentration range of 10(-1)-10(-4) M LiCl and the detection limits for all electrodes were ca. 5 X 10(-4) M. The response time of the electrode was faster at the higher lithium concentration and the response of the electrode was stable for longer than 6 months. The sensor membranes exhibit improved response times and increased lifetimes as compared to the system described earlier.