A new system for washing ion-exchange paper disks used in radiochemical enzyme assays.

A new device has been developed for the removal of radioactive substrate from ion-exchange paper disks, leaving ionized product bound to the paper. It has a number of important advantages over older methods of washing the ion-exchange paper: (1) It is much more thorough and efficient; background absorption of unionized material is reduced to relatively low levels. (2) Fragile media such as DEAE-substituted paper (DE81) are not subjected to the erosive effects of stirrers or agitators. (3) The disks remain organized throughout the sample application and washing procedure, eliminating need for time-consuming sorting of wet radioactive disks after washing. A larger number of assays can therefore be processed conveniently at one time. (4) Radioactive nucleosides and other adsorbable substrates are collected in a cartridge, eliminating the handling and sink-disposal of large volumes or excessive quantities of radioactive materials.