A Novel Approach for Rapid Screening of Stilbenes in Plant Extracts Based on SALDI Mass Spectrometry

Stilbenes are a class of plant phenolic secondary metabolites with a wide range of biological activity and pronounced antioxidant properties, which are important for various industries. This determines the urgency of developing new methods for identifying stilbenes in new plant sources. An original approach solving this challenge is proposed in this article.

Three standard samples of stilbenes rhaponiticin, isorhapontigenin, and polydatin were used to optimize the experimental conditions. Three plant extracts used for approbation were obtained by liquid extraction under pressure. Identification of stilbenes was conducted by surface-assisted laser desorption/ionization (SALDI) mass spectrometry using a quadrupole ion trap time-of-flight mass spectrometer, target plates with carbon nanocoating, and lithium cationization. Tandem mass spectra obtained by collision-induced dissociation (CID) were used for identification of stilbenes in the real objects.

Optimization of the conditions for obtaining mass spectra on standard samples allowed us to receive new knowledge about stilbenes fragmentation under SALDI: cleavage and addition of a water molecule in a quadrupole ion trap is characteristic for non-glycosylated compounds; cleavage of a hexose residue is a distinctive feature of glycosylated ones. Eight stilbenes, including glycosylated derivatives, were identified in spruce phloem, wild rosemary, and pine extracts that was confirmed by nuclear magnetic resonance (NMR) spectroscopy.

The proposed variation of SALDI mass spectrometry allows us to obtain high-quality stilbene tandem mass spectra suitable for subsequent identification in complex samples. The development of the approach makes it possible to analyze component composition directly in tissues, which will give an idea of the spatial distribution of secondary metabolites in plants.