LITHIUM DETERMINATION IN ARTIFICIAL SERUM USING FLOW-INJECTION SYSTEMS WITH A SELECTIVE SOLID-STATE TUBULAR ELECTRODE BASED ON NASICON MEMBRANES

The main objective of this work is the determination of lithium in the serum in the concentrations found in the plasma and the urine of pati ents being treated with lithium salts. Results of measurements under q uiescent conditions and with flow injection analysis are compared. The solid-state tubular lithium sensor evaluated is based on conductive c eramics. A flow injection analysis (FIA) system using Li+-NASICON as t he sensitive membrane and a BaCl2 0.1 M solution as carrier shows seve ral advantages such as a good sampling frequency (20 samples h(-1)), a low detection limit (logarithmic range from 5x10(-4) M) and a near-Ne rnstian sensitivity (57 mV/decade). Lithium measurements in artificial serum, using 0.1 M BaCl2 as a carrier solution, provided better resul ts. Lithium determination in urine is possible because the usual conce ntration (10-30 mM) is in the logarithmic response range of the sensor . Concerning blood analysis (from 7 x 10(-4) to 2 x 10(-3) M in Li), t he non-Nernstian response of the system in the lithium therapy concent ration range does not seem to be a major problem because of the system atic calibration possibilities when using I;LA instrumentation.