Natural Waxes Investigated by Soft Ionization Mass Spectrometry

Abstract

Field ionization (FI) and field desorption (FD) mass spectra of 35 aliphatic long-chain and branched long-chain compounds, representing the major six classes of constituents of natural waxes, are examined. In the FI mode the molecular ions are usually formed at comparatively low levels, while in FD such species are almost exclusively generated. In addition, some fast atom bombardment mass spectra, in the positive and negative ion mode, of selected lipids are recorded for comparison. In general, field ionization and field desorption techniques are found to be superior for mass spectrometric studies of low-polarity compounds. Examination of several natural waxes, such as Jojoba wax, preen gland wax of goose, beeswax and epicuticular wax of Norway spruce, shows that field desorption mass spectrometry has a most promising role in the characterization of wax components. The intense molecular ions allow the identification of the constituents of complex lipid mixtures without the need for derivatization. Thus, for the first time, the carbon number distribution, especially of the high-mass wax con­stituents can be established for the natural waxes investigated. For identification of high-mass wax constituents the present results suggest that field desorption mass spectra could be best employed in conjunction with class and individual separation of constituents by chromatographic proce­dures. The analysis of natural waxes is nowadays of major concern because of its importance in the problem of forest damage.