Analysis of kava resin by gas chromatography and electron impact and methane negative ion chemical ionization mass spectrometry. New trace constituents of kava resin

Abstract

Electron impact (EI) and methane negative ion chemical ionization (NICI) gas chromatographic/mass spectrometric analyses of kava resin, derived from commercial Piper methysticum, are described. The resulting mass spectra are correlated with the known major and trace constituents of this resin. Several of the kava lactones (kawain, methysticin, desmethoxyyangonin and yangonin) produced abundant molecular anions when analysed by methane NICI mass spectrometry, in contrast to their 7,8-dihydro analogues which ionized with poor efficiency to yield weak [M − H]− anions. Deuterium labelling established that the origin of the [M − CH3]− anion in the methane NICI mass spectrum of yangonin resulted from the elimination of a methyl radical from the 4-methoxyl substituent. As a result of the present study, an additional four trace components of kava have been identified.