Table 1.

Detection limits of underivatized estrogens with LC-negative APCI-MS.

Peak number	Estrogens	m/z	Avg LOD (µg/mL, n=5)
1	16-epiestriol	259.05 (18%), 287.10(100%)*, 288(38%), 317(10%)	6.60
2	16-keto-17β-estradiol	285.11(100%), 299.11(60%)	4.20
3	16α-hydroxyestrone	279.09(10%), 285.12(100%), 286.08(30%), 298.98(10%), 301.14(15%)	4.80
4	estriol	259.02(35%), 285.11(40%), 287.13(100%), 301.13(50%)	15.70
5	17-epiestriol	259.03(28%), 261.06(38%), 285.12(40%), 287.14(100%), 301.09(32%), 303.00(28%), 305.08(26%)	11.7
6	4-hydroxyestradiol	283.06(40%), 287.14(100%)	0.03
7	4-hydroxyestrone	285.11(100%)	0.05
8	2-hydroxyestradiol	285.07(40%), 287.10(100%), 288.11(50%)	0.014
9	2-hydroxyestrone	285.11(100%)	0.014
10	17β-estradiol	263(60%), 271(100%)	0.143
11	4-methoxyestradiol	259.03(60%), 275.00(100%), 286.10(70%), 301.16(75%)	19.2
12	2-methoxyestradiol	246.06(50%), 283.07(90%), 285.06(80%), 287.01(100%), 317.11(90%), 331.13(50%)	61.5
13	estrone	259.04(18%), 269.10(100%), 285.09(18%)	37
14	4-methoxyestrone	248.97(65%), 261.99(85%), 283.03(88%), 299.13(100%)	8.7
15	2-methoxyestrone	246.02(65%), 248.07(55%), 274.00(72(%), 284.07(90%), 299.01(100%), 331.17(40%)	32.4
16	2-hydroxyestrone-3-methyl ether	246.00(68%), 274.03(60%), 283.05(50%) 284.10(85%), 285.12(66%), 289.05(79%), 299.01(100%), 315.10(52%)	17.8

^*Underlined ions were used for detection limit determination.