A system and method of optically measuring Na.sup.+ and K.sup.+ in a sample such as blood which contains high concentrations Na.sup.+ (up to 160 mM) and K.sup.+ (up to 6.5 mM) using a photoluminescent probe having intrinsic analyte-induced lifetime changes. Specifically, the use of lifetime-based sensing of Na.sup.+ and K.sup.+ at the extracellular concentrations present in whole blood or, blood serum. The preferred embodiment uses phase-modulation fluorometry.
CROSS-REFERENCE TO RELATED APPLICATION
The present application is a continuation application of PCT/US99/05980, filed Mar. 19, 1999, which claims the benefit of U.S. Serial No. 60/111,554, filed Dec. 9, 1998.
