603957.fig.002a
(a) LC peak 1
603957.fig.002b
(b) LC peak 2
603957.fig.002c
(c) LC peak 3
603957.fig.002d
(d) LC peak 4
Figure 2: The mass spectra of the HPLC peaks of the cattle excrement treated at C. Mass scan was performed in negative ion detection mode after electrospray ionization. Theoretical ratios of mass to charge (m/z) of deprotonated ions ([M-H]-) of protocatechuic acid, vanillic acid, syringic acid and vanillin are 153.02, 167.03, 197.04, and 151.04, respectively.