Comparison of mass spectrometric ionization techniques for analysis of bioactive loline alkaloids

Loline alkaloids are a natural product of the endophyte complex Epichloë, which is commonly present in cool season grasses. These alkaloids, which may possess insect-deterrent and insecticidal activity, have previously been analyzed using gas chromatography-mass spectrometry GC-MS with electron ionization (EI). The purpose of this study was to develop an effective method for relative quantitation of loline alkaloids in endophyte-infected Achnatherum robustum (sleepygrass) samples. We compared three different analytical techniques, liquid chromatography coupled to electrospray ionization (UPLC-ESI-MS), liquid chromatography coupled to atmospheric-pressure chemical ionization (UPLC-APCI-MS), and GC-EI-MS. All three methods were effective for detecting the standard loline alkaloid N-acetylnorloline, but the best sensitivity and shortest analysis time was achieved using LC-MS techniques. UPLC-ESI and UPLC-APCI gave very similar detection limits, but greater fragmentation of the precursor ion was observed with APCI. Ultimately, our findings suggest that UPLC-APCI-MS may be a desirable alternative to GC-MS for profiling loline alkaloid content in endophyte-infected grasses.