DETERMINATION OF ZEATIN IN PLANT-EXTRACTS BY SQUARE-WAVE STRIPPING POLAROGRAPHY AND DIFFERENTIAL-PULSE STRIPPING POLAROGRAPHY

The electrochemical behaviour of the phytohormone trans-Zeatin at a ha nging mercury drop electrode was studied. Three adsorption waves are o bserved, the first is due to the complexation reaction between Hg(II), produced at the electrode, and Zeatin and the other two by specific a dsorption of Zeatin and reduction of the C=N group, respectively. The methodological and instrumental variables were studied in order to dev elop a determination method based on stripping differential pulse and stripping square wave polarography. The determination limits were betw een 15.5 and 53.6 ng ml(-1) and a linear variation of peak intensity v ersus Zeatin concentration was observed for the three waves. The proce dure was applied to the determination of Zeatin in plant extracts, aft er separation of cytokinins by means of a column packed with Amberlite XAD-I ion exchange resin. The proposed procedure was compared with th e determination by gas chromatography-mass spectrometry with prior met hylation of Zeatin.