Positive and negative ion chemical ionization mass spectrometry of trimethylsilyl derivatives of pyrrolizidine alkaloids using NH+ and OH− as the reactant ions

It is shown that the combination of positive ion and negative ion chemical ionization (PINICI) in gas chromatography/mass spectrometry of trimethylsilyl (TMS) derivatives of pyrrolizidine alkaloids (PAs) offers a rapid tentative structure elucidation of such compounds in plant material. PICI with NH3 as the reactant gas gives abundant [MH]+ ions; elimination of the necic acid produces a positive ion, corresponding to the necine base, which may carry a substituent at C7. NICI with OH− as the reactant ion cleaves the ester bonds, which may be present at C7 and C9 of the necine base or at the β‐C atom of the necic acid. This is illustrated by means of the fragmentation pattern of the PICI‐ and NICI‐mass spectra of echinatine‐(TMS)3 7‐acetyl‐lycopsamine‐(TMS)2, β‐acetyl‐echinatine‐(TMS)2, supinine‐(TMS)2 and curassavine‐(TMS)3 (or stereoisomers). In this way, a number of 7‐angelyl/tiglyl (e.g. symphytine), β‐angelyl/tiglyl and β‐(iso)valeryl (not reported before) derivatives of echinatine (or isomers like lycopsamine and intermedine) and of PAs with a saturated necine base, like trachelanthamine (or stereoisomers), could be shown in Symphytum taxa, Anchusa officianlis L. and Eupatorium cannabinum L.