High-performance liquid chromatographic separation of iodoamino acids for tracer turnover studies of thyroid hormones in vivo.

A reversed-phase high-performance liquid chromatographic technique was developed to separate radioiodinated thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3) and two diiodothyronines (3,3'-T2 and 3',5'-T2), in extracts from either serum or urine. Chromatography was performed with 10-micron C18 silica gel, packed in a glass column (3 X 300 mm); the mobile phase was methanol-water (55:45) adjusted to pH 3 with H3PO4, at a flow-rate of 1.2 ml/min and a pressure of 2800 p.s.i. The results demonstrate the ability of the system to yield a clear-cut separation of the iodothyronines involved in in vivo turnover studies, i.e., T4, T3, rT3, and the two T2 compounds together.