A method of radio-iodination on a submicrogram scale. The preparation and stability of 131I- and 125I-labelled 3-monoiodotyrosine and 3,5-diiodotyrosine of very high specific activity

Abstract 1. 1. 131 I- and 125 I-labelled monoiodotyrosine and diiodotyrosine with specific activities of around 2000 mC and 4000 mC, respectively per μmole have been prepared. 2. 2. A new iodination method on a submicrogram scale is described in which the solutions, separated by air bubbles, are assembled in a polytetrafluoroethylene capillary tube prior to their expulsion into the reaction vessel. The reaction is complete in 45 sec. 3. 3. The concept of ‘minimal specific activity’ and a routinely applicable method for its estimation is described. Simultaneously an estimation is obtained of the isotopic abundance in the radioiodide solution used for the iodination. 4. 4. The stability of these radioiodotyrosines was investigated. They are reasonably stable in the dark but unstable in ultraviolet light or under β-irradiation. Various substances accelerate or retard decomposition. There is a marked difference in behaviour between monoiodotyrosine and diiodotyrosine.