Table 1.

Repeatability (instrumental precision) and intra-day and inter-day precision data of the LC-ESI-MS/MS method for determination of phenolic acids.

Analyte	Nominal Concentration (ng/mL)	Repeatability (% CVa) (n = 10)	Precision
			Inter-day		Intra-day
			Measured Concentration (ng/mL)	CVa (%)	Measured Concentration (ng/mL)	CVa (%)
Gallic acid	167	4.7	152.5	4.9	156.6	2.1
	666	2.9	651.2	2.0	645	1.6
	3300	1.5	2899	0.9	2912	0.5
5-O-caffeoylqunic acid	17.65	2.2	15.0	2.4	14.9	3.3
	176.5	4.0	151.0	3.8	151.	5.3
	3530	1.2	3052	2.1	3077	2.1
Homogentisic acid	167	2.2	156.4	2.2	158.4	0.1
	1665	1.1	1477	0.5	1481	0.1
	11,100	2.4	10475	0.0	10,475	0.0
α-Resorcylic acid	347	2.9	337.8	4.7	339.1	6.5
	1735	5.0	1669	1.5	1663.7	2.0
	3470	4.2	3462	1.1	3443.3	0.8
Protocatechuic acid	347	3.6	299	2.5	301.3	3.3
	1700	2.1	1723	1.8	1716	2.4
	17,200	2.5	14,820	1.2	14,850	1.7
trans-Caffeic acid	350	2.7	314.7	4.7	322.9	1.8
	700	1.7	597.4	0.4	597.6	0.5
	3500	1.6	3015	2.8	3017	4.0
Syringic acid	666	4.9	589.6	0.8	592	0.7
	3330	2.8	2852	1.8	2855	2.5
	11,100	1.7	9510	1.3	9546	1.6
4-Hydroxybenzoic acid	347	3.5	283.0	4.7	275.8	2.6
	694	4.2	618.7	0.3	619.65	0.3
	3470	2.6	2975	0.5	2983	0.3
Vanillic acid	333	4.7	293.2	4.2	295.15	5.7
	1650	4.8	1439	1.3	1450	0.3
	33,000	2.0	30694	1.7	30,400	0.3
Gentisic acid	333	5.0	306.5	0.9	307.9	0.6
	1670	2.5	1914	2.5	1941	0.6
	3300	2.6	3653	1.9	3692	0.4
γ-Resorcylic acid	194	3.6	186.7	1.0	185.65	0.5
	1935	3.4	1873	1.3	1881	1.6
	7740	2.0	6648	1.3	6679	1.4
3-Hydroxybenzoic acid	667	2.3	590	1.6	593.4	1.9
	1334	2.6	1289	1.3	1298	0.1
	6670	1.6	6462	1.4	6487	1.7
β-Resorcylic acid	1970	3.4	1760	2.1	1781	0.7
	7860	0.5	6871	0.4	6885	0.1
	19,700	2.1	18180	0.4	18135	0.2
trans-Sinapic acid	69.4	4.3	78.3	1.0	78.8	0.0
	694	3.1	669	3.1	681.6	0.1
	3470	0.8	3026	2.7	3060	2.5
4-Hydroxycinnamic acid (p-coumaric)	373	3.8	322	2.8	319.1	2.9
	746	3.3	638	0.8	635.1	0.3
	3730	1.9	3476	2.3	3523	0.2
Ferulic acid	347	2.9	319.2	4.9	324.5	5.6
	1735	3.0	1663	1.0	1660	1.3
	11,600	2.1	10,508	1.2	10437	0.5
Rosmarinic acid	357	2.2	377.9	3.4	371.2	2.2
	1790	1.4	1685	1.3	1677	1.5
	7140	1.3	6982	0.8	7005	0.9
Isoferulic acid	343	4.9	299.8	4.8	299	6.8
	3430	1.8	3749	1.0	3738	1.3
	11,400	0.9	11627	0.2	11,625	0.3
3-Hydroxycinnamic acid (m-coumaric)	1740	2.0	1613	0.5	1617	0.4
	6940	3.2	6406	0.5	6387	0.1
	17,000	0.9	16,233	0.9	16,150	0.4
Veratric acid	3140	3.0	2931	2.4	2961	2.2
	15,700	1.5	15,403	0.5	15,375	0.5
	31,400	1.0	30547	0.3	30,487	0.1
3.4.5-Trimethoxyphenyl acetic acid	33.3	3.5	29.6	3.1	30	2.4
	333	1.9	362.5	4.0	361.9	5.6
	3330	0.6	3304	2.1	3341	1.3
2-Hydroxybenzoic acid (o-coumaric)	182	4.7	178.2	4.4	182.5	1.9
	1820	1.9	1859	3.7	1898	0.3
	3630	2.5	3728	0.5	3740	0.0
3.4-Dimethoxycinnamic acid	167	2.8	158.7	0.5	159	0.4
	1665	1.8	1444	1.7	1450	2.2
	11,100	0.7	10,738	0.8	10,687	0.2
Salicylic acid	330	4.6	362.2	4.4	370.5	2.5
	1650	0.5	1893	2.2	1914	1.5
	3300	2.6	3730	2.2	3773	1.3
3.5-Dimethoxybenzoic acid	1770	3.2	1693	1.3	1700	1.7
	7060	1.9	6416	0.4	6403	0.3
	35,300	3.9	30,072	2.2	30,075	3.2

CV^a —coefficient of variation.