DETERMINATION OF LOW CONCENTRATIONS OF LITHIUM IN BIOLOGICAL SAMPLES USING ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A method is described for the determination of endogenous lithium concentrations in serum and urine using electrothermal atomic absorption spectrometry. The method has also been applied to the analysis of nanolitre samples of micro-puncture fluid from rat kidney tubules containing pharmacological concentrations of lithium. The graphite tubes are coated in situ with tantalum to give improved sensitivity and increased pre-atomization stability. A mini-flow of gas at a flow-rate of 30 ml min-1 is used during atomization to eliminate background interference. Background correction is not necessary. The characteristic mass is 0.98 pg of lithium. Serum samples are deproteinized with an equal volume of 10% nitric acid before analysis. Urine samples are diluted 5-fold with 5% nitric acid. The normal range of serum lithium is up to 0.39-mu-mol l-1 and normal urinary excretion is up to 9-mu-mol over a period of 24 h.