Table 5.

Stability of quality control samples

Compound	Nominal Concentration (ng/mL)	Mean measured concentration (ng/mL)
		autosampler at 4 °C, 72h	long storage −20 °C, 2 months
Equol	50	43.35 ± 2.50	45.68 ± 3.98
	500	487.80 ± 9.20	475.66 ± 30.16
	2000	1793.33 ± 67.42	1921.66 ± 94.74
Daidzein	50	47.03 ± 2.50	50.83 ± 1.87
	500	534.20 ± 21.05	491.66 ± 7.17
	2000	1848.33 ± 72.77	1861.66 ± 71.67
Dihydrodaidzein	50	45.55 ± 1.97	47.52 ± 5.23
	500	485.83 ± 26.35	219.20 ± 15.90
	2000	1738.33 ± 85.18	828.50 ± 27.01
O-DMA	50	48.31 ± 3.75	54.80 ± 5.67
	500	469.16 ± 24.01	534.66 ± 28.57
	2000	1861.66 ± 114.61	2151.66 ± 110.89
Genistein	50	50.90 ± 3.19	51.16 ± 3.34
	500	487.33 ± 33.15	497.33 ± 37.59
	2000	1875.00 ± 116.40	2190.00 ± 11.83
Glycitein	50	44.31 ± 2.44	40.15 ± 1.98
	500	481.00 ± 39.11	489.50 ± 28.26
	2000	1886.66 ± 87.10	2045.00 ± 191.91
Formononetin	50	47.36 ± 4.16	47.58 ± 3.22
	500	512.33 ± 26.41	507.66 ± 27.82
	2000	2018.33 ± 106.09	1925.00 ± 167.06
Coumestrol	50	46.26 ± 6.68	56.80 ± 2.37
	500	549.33 ± 36.74	498.00 ± 26.1
	2000	2120.00 ± 104.30	1905.00 ± 128.17
Biochanin A	50	52.47 ± 2.27	56.10 ± 1.49
	500	444.00 ± 29.81	523.00 ± 23.34
	2000	1893.33 ± 202.06	2130.00 ± 88.31
Enterodiol	50	44.96 ± 3.45	46.84 ± 2.47
	500	488.16 ± 13.04	489.83 ± 20.79
	2000	1906.66 ± 68.89	1963.33 ± 119.27
Enterolactone	50	52.20 ± 3.27	48.73 ± 6.55
	500	495.50 ± 16.92	484.66 ± 34.44
	2000	1801.66 ± 75.70	1678.00 ± 66.55