Assay of tritium-labelled terbutaline

A method for the determination of unchanged 3H-labelled terbutaline in biological samples was developed for use in early pharmacokinetic investigations involving various species. Terbutaline was isolated from the biological sample by ion pair extraction with 0.015 mol/L bis(2-ethylhexyl)phosphoric acid in methylene chloride. To eliminate co-determination of conjugated terbutaline present in the samples, extraction was combined with partition chromatography. Quantification was achieved by liquid scintillation counting. The recovery of [3H]terbutaline from serum and urine was 96.1 +/- 0.7 (mean +/- SEM) in the concentration range 1-250 ng/mL.