Differentiation between isomeric methylated purine derivatives by means of chemical ionization and collision‐induced dissociation

A number of commercially available purine derivatives were investigated by means of chemical ionization in ammonia and methane reagent gases. The protonated molecules of the compounds investigated were mass selected and their collision‐induced dissociated (CID) spectra monitored using 100 eV collision energy. Competition between the protonation and addition reaction channels which yield MH + and [M + NH 4 ] + ions and the major fragment ions observed in the CID spectra reflect certain stereochemical differences between the isomeric precusors investigated. The present work is an attempt to contribute to the continuous search for first and effective means of distinguishing between the various isomers of biomedically important classes of compounds.