Identification of phenolic compounds in Eugenia uniflora leaves by FTICR MS in association with different ionization sources

Abstract

Eugenia uniflora leaves are a rich source of phenolic compounds with biological activities. In this study, the chemical profile of samples obtained from three sample preparation methods, liquid/liquid extraction from a methanol extract of the leaves (LLE), solid phase dispersion of the leaves in silica gel (SE_Si) and direct mass analysis on the cleaned leaf surface (LMDA), was evaluated from spectra generated by ultra-high resolution mass spectrometry (Fourier Transform Ion Cyclotron Resonance, FT-ICR) coupled with three different ionization methods, electrospray (ESI), paper spray (PS), and leaf spray (LS). Several flavonoids and phenolic acids were detected in their deprotonated form in the regions from m/z 150 to 1300. Myricitrin ([C₂₁H₂₀O₁₂ − H]⁻, m/z 463.08831, 0.24), its chloride adduct ([C₂₁H₂₀O₁₂ + Cl]⁻m/z 499.06499, 0.11) and other myricitrin derivatives, gallic acid ([C₇H₆O₅ − H]⁻, m/z 169.01415, 0.58) and O-methyl gallic acid ([C₈H₈O₅ − H]⁻, m/z 183.02998, 0.47), were the main compounds detected. Generally, the use of the ESI(−) source is considered the best ionization method along with LLE as the sample preparation method, producing more intense signals in the mass spectra of myricitrin and its derivatives. LS is an ionization method with negligible sample preparation, but in this case, it provided less intense signals for the compounds of interest when compared to ESI(−)MS. Considering phenolic compounds of Eugenia uniflora, electrospray proved to be the most efficient mass ionization method for the identification of biologically active substances.