**4. Conclusions**

In this study, five flavonoid glycosides of eriocitrin, narirutin, hesperidin, rutin, and diosmin in lemonade were identified and determined by UPLC-TOF/MS and UPLC-QqQ/MS, respectively. By estimating the content characteristics of flavonoid glycosides in the samples, we highly suspected that some lemonade available in the market was counterfeited: Cheap rutin was added to increase the content of "total flavonoids of lemon". This indicates that besides using total flavonoids, the content of multiple flavonoid compounds should be included in the quality standard of lemonade in the future.

**Author Contributions:** Conceptualization, L.-S.Q. and J.X.; Data curation, Y.X.; Formal analysis, Y.X. and M.-Q.T.; Funding acquisition, L.-S.Q.; Methodology, Y.X.; Project administration, J.X.; Resources, L.Y., B.H., and X.-S.X.; Supervision, L.Y., B.H., X.-S.X., and J.X.; Validation, Y.X.; Writing—original draft, L.-S.Q.; Writing—review & editing, J.X.

**Funding:** Financial support was provided by the West Light Foundation of The Chinese Academy of Sciences (No. 2018XBZG\_XBQNXZ\_A\_005).

**Conflicts of Interest:** The authors declare no conflict of interest.
