DETERMINATION OF CYTOKININS BY MASS-SPECTROMETRY BASED ON STABLE ISOTOPE DILUTION

A method for quantitative determination of individual cytokinin species has been developed, based on gas chromatography-mass spectrometry and selected ion monitoring. Deuterated internal standards were prepared for analysis of N6-isopentenyladenosine, N6-isopentenyl-2-methylthioadenosine, zeatin riboside, and 2-methylthiozeatin riboside and were tested over the range of 1 to 20 ng of endogenous cytokinin per injection, relative to 100 ng of labeled standard. An isolation procedure for extracts of cabbage hearts as a model plant source has been developed that gives maximum recovery and minimum interference for gas chromatographic-mass spectrometric measurements. The present method differs from the commonly used bioassay by its selectivity for individual cytokinin components and shortened analysis time, including extractions, of 3 days vs several weeks. © 1979.