Table 2. TMS-Derivatized Sapogenin Aglycones Identified in Switchgrass Extracts by CI GC–MS Analysis^a.

peak	retention index (RI)b	key ion annotations (m/z)c	abundant fragment ion m/zd	formula of the neutral molecule	mass of the neutral molecule (Da)	annotation of the neutral moleculee
D1	3114	397 [M + H]+	139, 282	C27H40O2	396	anhydro-diosgenin
D2	3194	397 [M + H–TMS–OH]+, 471 [M–CH3]+, 485 [M – H]+, 487 [M + H]+	139, 282	C30H50O3Si	486	diosgenin (TMS-derivatized)
D3	3339	397 [M + H–TMS–OH]+, 471 [M–CH3]+, 485 [M – H]+, 487 [M + H]+	139, 187, 282	C30H50O3Si	486	diosgenin (TMS-derivatized)
D4	3361	397 [M + H–TMS–OH]+, 471 [M–CH3]+, 485 [M – H]+, 487 [M + H]+	139, 187, 282	C30H50O3Si	486	diosgenin (TMS-derivatized)
T1	3399	409 [M + H–TMS–OH]+, 483 [M–CH3]+, 497 [M – H]+	218, 203, 190	C33H58OSi	498	β-amyrin (TMS-derivatized)
T2	3439	409 [M + H–TMS–OH]+, 483 [M–CH3]+, 497 [M – H]+	218, 203, 190	C33H58OSi	498	β-amyrin (TMS-derivatized)
O1	3462	395 [M + H–TMS–OH–H2O]+, 413[M + H–TMS–H2O]+, 487 [M–CH3]+, 501 [M – H]+, 503 [M + H]+	139, 187, 298	C30H50O4Si	502	oxydiosgenin (TMS-derivatized)
O2	3620	395 [M + H–TMS–2H2O]+, 413[M + H–TMS–OH]+, 487 [M–CH3]+, 501 [M – H]+, 503 [M + H]+	139, 187, 298	C30H50O4Si	502	oxydiosgenin (TMS-derivatized)

^aThe TMS-derivatized molecules are considered as the molecular ions in each case here. TMS, trimethylsilyl group [Si(CH₃)₃].

^bThe RIs were calculated using a homologous series of n-alkane standards with the same GC–MS method as employed for the samples (Figure S4A).

^cThe m/z information for the key ion annotations was obtained by (CI) GC–MS (Figure S62).

^dThe m/z information for the fragment ions was obtained by electron ionization (EI) GC–MS (Figure S4B).

^eThe annotations were made based on the pseudomolecular ions and fragment ion information from (EI) MS (Figure S4B) by comparing with the diosgenin standard and/or searching against the National Institute of Standards and Technology (NIST) NIST17 GC–MS library (www.chemdata.nist.gov) for the best matching compounds.