SODIUM ION-SELECTIVE ELECTRODES BASED ON DIBENZO-16-CROWN-5 COMPOUNDSWITH PENDENT AMIDE GROUPS

Potentiometric selectivities for alkali-metal cations of dibenzo-16-cr own-5 compounds with amide-containing side arms attached to the centra l carbon atom of the three-carbon bridge have been determined in solve nt polymeric membrane electrodes. The lariat ethers include N-alkyl- a nd ,N-dialkyl-sym(R)-dibenzo-16-crown-5-oxyacetamides with R = hydroge n or an alkyl group. The presence of an alkyl group on the ring carbon which bears the amide-containing side arm markedly increases the Na+/ K+ selectivity of poly(vinyl chloride) matrix membrane electrodes with o-nitrophenyl octyl ether as the membrane solvent. Lariat ethers with a N,N-dipentyloxyacetamide group as the side arm and a geminal alkyl group of two or more carbon atoms exhibit high Na+/K+ selectivities (l og K-Na,(Pot)(K) = - 2.1) with good selectivities for Na+ over the oth er alkali-metal cations, H+, NH4(+), and alkdine-earth-metal cations.