Method of comparing radioactive concentration

A method is described for comparing the radioactive concentrations of liquids in a set of vessels. The method comprises the following steps: (a) drawing liquid from one of the vessels into a measuring region, so that the liquid fills the region, (b) measuring the radiation from the liquid in the region, (c) expelling the liquid from the region and (d) repeating steps (a), (b) and (c) with the liquid in each of the vessels and comparing the radiation measurements. This technique may form part of an analysis involving several vessels each containing a radioactive element or compound partitioned between two phases. Typical of such analyses are assays of the kind in which an unknown amount of the compound to be assayed and a standard amount of a labelled version of the compound compete for reaction with a standard amount of a specifically reacting reagent. The method is widely used in the medical field for assaying hormones and other medical substances, using as the other reagent the antibody in immune systems or some other reacting substance such as a specific binding protein, in non-immune or non-hormone systems. Suitable apparatus is described. (U.K.)