Determination of phenolic compounds in Chinese poplar propolis, Brazil green propolis, and poplar gum by high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry and preliminary study of the identification of adulteration

High-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (HPLC/Q-TOF MS) was used to analyze 23 phenolic compounds in Chinese poplar propolis, Brazil green propolis, and poplar gum. Propolis and poplar gum samples were dissolved in methanol-water (1:1, v/v) and filtered by 0.45 μm organic phase filtration membrane. The separation was carried out in an Agilent Eclipse Plus C18 column with gradient elution using acetoni-trile and 0.1% (volume percentage) formic acid solution as the mobile phases. The compounds were detected using positive ion electrospray ionization in full scan mode (m/z 100-1000). The quantification analysis was performed by the external standard method. The results showed that all the compounds were linear, with correlation coefficients>0.99, in the range of 10-20 μg/L. The limits of detection and limits of quantification for tangeretin and formononetin were 0.2 and 1 μg/L, respectively, and those for the other compounds were 2 and 10 μg/L, respectively. At the spiked levels of 10, 25, and 50 mg/kg, the recoveries of all the compounds ranged from 70.2% to 122.6%, with relative standard deviations of less than 10%. Salicin, cinnamic acid, caffeic acid, and coumaric acid could be used as markers for detecting adulteration in Chinese poplar propolis, while caffeic acid, ferulic acid, chrysin, caffeic acid phenethyl ester, pinocembrin, galangin, coumaric acid, isorhamnetin, kaempferide, and arte-pillin C could be used as markers for identifying Chinese poplar propolis and Brazil green propolis. The results presented in this paper may be helpful in quality control of propolis products.