Thin layer chromatographic identification of phenothiazine derivative drugs: interlaboratory study

A thin layer chromatographic method for the identification of phenothiazine derivative drugs was studied collaboratively by 8 laboratories. Twenty phenothiazine drugs were examined by each collaborator. The identification scheme depends on the color of the sprayed spots and the Rf values relative to the Rf of chlorpromazine (RCHL) in 4 solvent systems. In 98.13% of the cases, a correct identification could be made; the remaining drugs were reduced to a choice between pairs of phenothiazines. With respect to chlorpromazine, the data showed a significant decrease in variability of RCHL values compared with Rf values in the 4 solvent systems.