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A high-performance liquid chromatograph with a synchronized accumulating radioisotope detector was used to determine the turnover rate and pool size of tryptophan in rat. The specific radioactivity could be followed for three half-lives on the final slope of the specific radioactivity curve following intravenous administration of 15 muCi of carrier free tryptophan labeled with carbon-14. Remarkable individual differences were noted in turnover rate and in pool size among rats.

The synthesis and properties of 2-[125I]-lysergic acid diethylamide, the first 125I-labeled serotonin receptor ligand, are described. A novel microsynthesis apparatus was developed for this synthesis. The apparatus employs a micromanipulator and glass micro tools to handle microliter to nanoliter volumes on a microscope stage. This apparatus should be generally useful for the synthesis of radioligands and other compounds when limited amounts of material must be handled in small volumes.

A simple, one-step spectrofluorometric method for determination of terbium is described. The technique requires a single addition of dipicolinic acid to a terbium-containing solution, is sensitive to 10 n m Tb3+, and is independent of pH in the range 5.0–10.5. The method, applicable in several buffer systems and in the presence of large concentrations of alkali metals, is applied to the determination of Tb3+-apoconcanavalin A association constants.