Study of Nettle (Urtica dióica) Lignin by Atmospheric Pressure Photoionization Orbitrap Mass Spectrometry

Abstract

Orbital ion trap high-resolution mass spectrometry with acetone doped atmospheric pressure photoionization is first used to characterize the structure of grass lignins using an example of nettle (Urtíca dióica) dioxane lignin. The obtained mass spectrum contains about 3,000 peaks of deprotonated molecules of lignin oligomers in the molecular mass range up to 1.6 kDa. The study of tandem mass spectra and of a composition of monomers formed in the collision-induced dissociation of lignin macromolecules showed the special role of p-hydroxycinnamic acids in the formation of nettle lignin. Based on the results of tandem mass spectrometry, possible structures of nettle lignin oligomers formed by the addition of guaiacyl- and syringylpropane units followed by etherification by p-coumaric, ferulic, and dihydroferulic acids are proposed.