Determination of 75Se-labelled selenite and metabolites in plasma and urine by high-performance liquid chromatography with on-line radioactivity detection.

A reversed-phase ion-pair high-performance liquid chromatographic method with on-line radioactivity detection for the simultaneous determination of 75Se-labelled selenite and metabolites has been developed. With this system a good resolution of various radiolabelled selenium complexes can be achieved. The detection limit of the radioactivity detector (signal-to-noise ratio = 3) is 49 pg of selenium (specific activity of 3 GBq/mg selenium) per millilitre of urine or plasma ultrafiltrate. The detector response is independent of both the chemical structure of the selenium complexes and the matrix composition of the samples. This method may serve as a reference system for other high-performance liquid chromatographic systems with less specific and sensitive detectors.