TABLE 1.

Phenolic acids quantified by UPLC-MS in rhizosphere soil around maize and soybean.

Analytes	RT (min)	Transition	CV (v)	CE (v)	Molecular weight	Actual concentration (μg/g)
						Maize	Soybean	Control
p-Hydroxybenzoic acid	0.85	136.968>93.476	28	32	137	17.11 ± 0.78a	3.29 ± 1.43b	0.82 ± 0.38c
p-Coumaric acid	1.34	162.968>119.468	28	32	164	26.13 ± 0.12	–	–
Cinnamic acid	2.80	147.032>76.967	26	30	148	0.15 ± 0.02	–	–
Vanillic acid	0.97	166.968>151.995	14	30	168	4.93 ± 0.13a	1.55 ± 0.10b	0.11 ± 0.02c
Ferulic acid	1.56	193.032>133.979	16	30	194	0.51 ± 0.00b	2.16 ± 0.06a	0.04 ± 0.02c

RT, retention time; CV, cone voltage; CE, collision energy. Control, soil without plant culture. The error indicates the standard errors of the means (n = 3). Significant differences are based on ANOVA tests. Lower case letters show significant differences in the same phenolic acids at the soil with different plant culture at the 0.05 level.