“…The negative ion mode was much more suitable for the analysis of this kind of compounds. Except for methyl gallate (21), ethyl gallate (32), protocatechuic aldehyde (18) and succinic acid (4), other 13 phenolic acids including gallic acid (8), protocatechuic acid (13), neochlorogenic acid (16), chlorogenic acid (19), p-hydroxybenzoic acid (20), vanillic acid (24), 2-methoxycinnamic acid (25), caffeic acid (27), 4-hydroxycinnamic acid (35), ferulic Acid (39), 3-hydroxycinnamic acid (45), 2-hydroxycinnamic acid (54) and cinnamic acid (65) had one carboxylic group in their structures, and their characteristic fragmentation behavior was the loss of CO 2 (44 Da) (take cinnamic acid as an example, Fig. 3C).…”