Stable isotopes for determining biokinetic parameters of tellurium in rabbits.

We have compared the use of stable and radioactive isotopes for determining the concentration of tellurium in body fluids of animals and man, specifically in the blood plasma of rabbits. Particular effort has been devoted to developing a sample-processing technique that allows the total amount of tellurium and isotope ratios to be measured by graphite furnace atomic absorption spectrometry (GFAAS) and secondary ion mass spectrometry (SIMS), respectively. The procedure employed in the SIMS analysis is discussed in detail. Investigations on the plasma clearance and the fractional intestinal absorption were carried out on four rabbits. Tracer solutions containing stable tellurium enriched in 124Te or 126Te and radioactive tellurium (121mTe or 123mTe) were administered by gavage and/or intravenously. Blood samples were drawn during the first 2 days after application. The activity of the separated plasma was measured by standard gamma ray spectrometry. After wet ashing and solvent extraction with MIBK the samples were analyzed for stable tellurium. A detection limit of 1 ng/mL of plasma could be achieved with GFAAS. For SIMS analysis the processed samples were deposited on high-purity graphite backings. Reliable isotope ratios could be determined with sample fractions containing 1 ng of tellurium or even less. The results obtained by applying stable isotopes were found to be in good agreement with the data achieved by using radioactive tracers. Studies on the intestinal absorption and the metabolic behavior of tellurium in human volunteers may thus be performed with stable isotopes.