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 Zeta mays kernels where the levels of endogenous zeatin, zeatin-9p-riboside and zeatin-9~-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.

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In contradiction of long-accepted mass spectrometric dogma, the site-specific y-hydrogen rearrangement is observed in alkylbenzenes in which both ortho positions are blocked with methyl substituents. Mass spectrometric studies of a series of five trimethyl-and three tetramethylisopentylbenzenes have shown that this rearrangement is only suppressed to a significant degree in those compounds in which all three positions ortho and para to the isopentyl group are blocked. Deuterium labelling has confirmed the y-site-specific origin of the migrating H atom while metastable studies have been used to investigate the mechanism of the rearrangement process.

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