Evaluation and application of magnetizable charcoal for separation in radioimmunoassays

We compared conventional charcoal separation of antibody-bound and free antigen with a novel method involving magnetizable particles containing charcoal. The magnetizable charcoal separation method was as effective as the conventional method for a wide range of radioimmunoassays, including those for several steroids and small polypeptide hormones. In a detailed comparison of conventional vs. magnetizable charcoal for radioimmunoassay of aldosterone, the magnetizable charcoal had several advantages: it did not require prior coating with dextran or protein, varied less with time and temperature, required no centrifugation, and took less time for separation. The correlation of results obtained with magnetizable and conventional charcoal separation was excellent (n = 89, r = 0.98, p less than 0.001), and the coefficient of variation for the separation with magnetizable charcoal was 0.5%.