[en] Flash pyrolysis of organic acids or of their salts gives off carbon dioxide which can be analysed by mass spectrometry for ¹³C and ¹⁸O abundance. This principle has been applied to Cd¹³C¹⁸O₃ using an induction furnace, and used to determine the ¹³C and ¹⁸O content of the carboxylic group of some amino acids. The technique described has many advantages over the classical pyrolysis methods using sealed tubes. It is rapid and simple and especially effective in determining the isotopic composition of hygroscopic carboxyl substances. (U.K.)