Strategy to rapidly discriminate trace isomeric lignan compounds from Gymnotheca chinensis by probe electrospray ionization tandem mass spectrometry.

Probe electrospray ionization (PESI) is a recently developed ionization technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid needle. High tolerance to salts, requirements of a trace amount of sample and direct ambient sampling- are major advantages of PESI compared with conventional ESI. In this report, three pairs of isomeric lignans bearing tetra-hydrofuran with variable conformations from Gymnotheca chinensis were investigated by probe electrospray tandem mass spectrometry (PESI-MS/MS) in the positive ion mode. The diagnostic characteristics of these compounds were obtained and the isomers could be successfully distinguished by comparison with their breakdown curves, even though the isomers differed only in the conformation of some groups of the isomer pairs. This report provides a rapid and reliable method for the identification of trace amounts of isomeric lignans by PESI-MS/MS. Furthermore, application of PESI and breakdown curves should have value in mass spectrometry studies of isomeric natural products compounds.