Monitoring radioactive compounds in high-performance liquid chromatographic eluates: fraction collection versus on-line detection.

This study compared two methods of monitoring radioisotopes in high-performance liquid chromatographic eluates (on-line radioactivity detector versus fraction collection and counting). Testing was accomplished by pumping solutions of tritiated water in acetonitrile--water mixture through the detector or to the fraction collector. At most solvent compositions, the detector's counting efficiency and detection limits were poorer than those of the scintillation counter. However, the reproducibility of the detector data was superior at acetonitrile concentrations of less than 50%. This was attributed to the difficulty in collecting fractions of small equal volumes at the lower organic solvent concentrations in short time intervals. We conclude that on-line monitoring with homogeneous detection is the preferred method for detecting radiolabeled compounds in high-performance liquid chromatographic eluates.