COMPOSITIONAL ANALYSIS OF INTACT ALKYL ESTERS IN LEAF EPICUTICULAR WAX OF SWEDE BY CAPILLARY GAS-CHROMATOGRAPHY AND ELECTRON-IMPACT MASS-SPECTROMETRY

A method for the separation and identification of complex mixtures of more than 50 different intact esters in epicuticular wax of swede, Bra ssica napus var. rapifera cv. Doon Major, using combined gas chromatog raphy-mass spectrometry (GC-MS) has been developed. The esters were se parated at temperatures of up to 350 degrees C by automatic pressure p rogramming (for capillary GC) or by manually increasing helium carrier gas pressure (for GC-MS) in order to maintain Bow at high temperature s. Esters in the range C-41-C-50 were detected, with regular repeating acid/alcohol combinations. Individual acid and alcohol moieties were identified from [RCO(2)H(2)](+) ions in the mass spectra of intact est ers and, following trans-esterification and silylation, from the mass spectral and chromatographic characteristics of the methyl esters of t he acid components (C-14-C-23) and trimethylsilyl derivatives of the a lcohol components (C-23-C-31) The major compounds were doubly branched C-44 and C-46 esters, composed of anteiso-C17/anteiso-C-27 (32.7%), a nteiso-C-17/anteiso-C-29 (11.9%) and anteiso-C-19/anteiso-C-27 (13.1%) acid/alcohol combinations, respectively, singly branched C-43 and C-4 5 esters, composed of n-C-16/anteiso-C-27 (8.5%), anteiso-C-17/n-C-26 (3.9%), n-C-18/anteiso-C-27 (6.8%), anteiso-C-17/n-C-28 (2.3%) and ant eiso-C-19/n-C-26 (1.6%), were minor components.