Table 1.

UHPLC retention times (RT), negative ion electrospray MS/MS selected reaction monitoring (SRM) transitions, collision energies (CE), and concentrations (ng/mL) of standards spiked into blank human serum for calibration curves^a

				Spiked concentrations (ng/mL)
Analyte	RT (min)	SRM transition m/z	CE (V)	(1)	( 2 )	( 3 )	( 4 )	( 5 )	( 6 )	( 7)	( 8 )	( 9 )	( 10 )	( 11 )
Silychristin	1.9	481 → 125   481 → 325	29   22	1.2	2	4	8	16	32	64	128	256	512	1024
Silydianin	2.4	481 → 179   481 → 125	26   31	1.2	2	4	8	16	32	64	128	256	512	1024
Silybin A	5.1	481 → 125   481 → 301	28   21	0.4	2	4	8	16	32	64	128	256	512	1024
Silybin B	5.5	481 → 125   481 → 301	29   21	0.4	2	4	8	16	32	64	128	256	512	1024
Isosilybin A	6.9	481 → 125   481 → 453	29   20	0.4	2	4	8	16	32	64	128	256	512	1024
Isosilybin B	7.2	481 → 125   481 → 453	27   19	0.4	2	4	8	16	32	64	128	256	512	1024
d4-Daidzein	3.6	257 → 212   257 → 136	31   39

^aThe first SRM transition of each milk thistle flavonolignan was used as the quantifier while the second SRM transition was used as a qualifier in the UHPLC-MS/MS assay.