Radioactive labelling of unsaturated compounds with 125I and 131I for analysis by thin-layer chromatography

It is demonstrated that unsaturated compounds can be determined by iodination procedures with radioactive iodine. Fatty acids and barbiturates with unsaturated side-chains were used as model systems. The detection limits obtained with this procedure at a signal-to-noise ratio of 3:1 are 20 ng of butalbital per spot using 125I and 5 ng per spot with 131I. The reproducibility of these techniques is ca. 2% (relative standard deviation) for concentrations greater than 0.5 μg per spot and ca. 4% or higher for amounts less than 0.1 μg per spot. The method is generally applicable to a number of unsaturated compounds; others, such as ergotamine and codeine, exhibit some uncontrolable secondary reactions and therefore cannot be measured. In general, the reaction is additive, i.e., the number of double bonds determines the sensitivity of the method. (Auth.)