Lithium-6 stable isotope determination by atomic absorption spectroscopy and its application to pharmacokinetic studies in man.

No useful radioisotope of lithium exists to assist in the study of its biochemical pharmacology. A simple method has been developed for the determination of the stable isotope 6Li by atomic absorption spectroscopy (AAS). The technique is applicable in any laboratory equipped with simple AAS apparatus. Analysis of total lithium content (E) by flame emission spectroscopy is followed by separate determination (A6 and A7) of atomic absorption by the sample of the light emitted by separate hollow cathode lamps manufactured from the isotopes 6Li and 7Li. The standard curve of absorption ratio (A6/A7) against isotopic ratio (6Li/7Li) at any concentration (E) is an exponential which may be solved using a simple programmable calculator. Application of this method to the study of the pharmacokinetics of 6Li administered to 4 normal volunteers previously loaded with 7Li suggests that the rate of appearance of lithium in blood is unaffected by the previous state of lithium loading.