Mass spectrometric analysis of cytokinins in plant tissues. II—Quantitation of cytokinins in Zea mays kernels using deuterium labelled standards

Deuterium labelled analogues of the major zeatin derived cytokinins have been synthesized to serve as internal standards for mass spectrometric quantitation. A procedure for the isolation, high performance liquid chromatographic purification and direct probe mass spectrometric analysis of these cytokinins has been devised and applied to the analysis of Zea mays kernels where the levels of endogenous zeatin, zeatin‐9β‐riboside and zeatin‐9β‐glucoside were estimated by isotope dilution. Additionally, the deuterated compounds have been utilized to confirm the identity of the in vitro enzymic glucosylation products of zeatin.