The method developed for the determination of the optical purity of L-selenomethionine-75Se is based on the conversion of the mixture of L-and D-amino acids into the diastereoisomeric derivatives by reaction with
(−)-camphorsulphonyl chloride. The diastereoisomeric derivatives are separated by means of thin layer chromatography. From
the ratio of the radioactivities of the two spots on the chromatogram, the optical purity is calculated, and given in % D.
For a sample of L-methionine-14C the following value was found: 0.53±0.05 (S.D. of mean, n=7). For a sample of DL-methionine-14C the percentage of D found, was: 48.5±0.5 (S. D. of mean, n=7). Of 30 different samples of L-selenomethionine-75Se the percentages of D-isomer were determined in duplicate. From the 30 differences between duplicates the S. D. of a single
measurement is calculated to be 0.2.