Abstract: An electrochemical sensor with a gelled membrane for prolonging the useful life of an ion-selective electrode. The gelled membrane is a hydrophilic membrane having a specially-formulated gel layer coated on one side. The gel-coated side of the gelled membrane is in intimate contact with the ion-selective membrane and separates the ion-selective membrane from the test samples and the calibration and cleaning fluids. The gelled membrane is a semi-permeable barrier which allows passage of the species to be measured while inhibiting the passage of surfactant and proteinaceous material into the polymeric ion-selective membrane.

Abstract: The magnesium ion content of a sample is determined by contacting the sample with a magnesium ion selective membrane including a 1,10-phenanthroline having an H group at positions 2 and 9. Examples of preferred 1,10-phenanthrolines include 4,7-diphenyl-1,10-phenanthroline, N-dodecyl-N-methyl-1,10-phenanthroline-4-carboxamide, 4-undecyl-1,10-phenanthroline, 4,7-diundecyl-1,10-phenanthroline and 5-nonyl-1,10-phenanthroline-4-carboxylate.

Abstract: An electrode for determining the lithium content of a liquid sample to be tested, has a membrane containing a lithium ion selective compound and a plasticizer, the improvement wherein the plasticizer is a liquid, lipophilic dialkyl phthalate compound or a liquid phenyl phenyl ether compound that has a strong electron withdrawing group at an ortho position on one of the phenyl rings. The ion selective compound has the formula: ##STR1## wherein A is an alkyl group having between 8 and 16 carbon atoms, B is an alkyl group having between 1 and 4 carbon atoms, and each C and D is, independently, a hydrogen atom or an alkyl group having between 1 and 16 carbon atoms, provided that both C and D are not alkyl groups having greater than 4 carbon atoms.