Trace enrichment and characterization of polyphenols in Bistort Rhizoma using weak anion-exchange solid phase extraction and high performance liquid chromatography-quadrupole time-of-flight mass spectrometry

• Polyphenols were selectively enriched by a weak anion-exchange SPE.
• MS/MS fragmentation rules of polyphenols were outlined.
• Twenty six trace members were identified for the first time in this herb.

The analysis of trace constituents in herbal medicines has always been a challenge due to complex matrices and structural diversities. In this work, a pH-sensitive solid phase extraction (SPE) procedure capable of enriching trace polyphenols in Bistort Rhizoma (BR) was proposed and preliminary chemical characterization was accomplished by high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-QTOF MS). A weak anion-exchange SPE column packed with divinylbenzene/vinylpyrrolidone bonding quaternary amine group was employed for anionic extraction, and the target fraction was obtained by eluting with acidic methanol (apparent pH 1.9). On the other hand, the MS/MS fragmentation rules of four reference polyphenols in negative ion mode were outlined. Using these rules, a total of 31 polyphenols including 20 benzoyl derivatives and 11 caffeoyl derivatives were screened out from BR extract, of which 26 trace members were found for the first time in this herb. Those findings demonstrated that the anion-exchange SPE could enhance the detection capability and selectivity for plant polyphenols in the LC–MS analysis and the strategy for deducing structures could be applied for analysis of polyphenols in BR and other herbal medicines.

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