Table 2.

Protonated molecular ions in APCI mass spectra of tentatively identified GDGT XIII–XV and pseudo Kovats indices and diagnostic ions in electron mass spectra of the carbon skeletons released by HI/LiAlH₄ degradation of these GDGTs (see Fig. 1)

GDGT*	[M+H]+†	Carbon skeleton*	RImeasured	RIcalculated‡	Diagnostic ions mass spectrum hydrocarbon
XIII	1020	f§	2912	2914	196/197, 253
		h	2945	—¶	193/194/195/196, 210, 251, 420
XIV	1018	h	2945	—	193/194/195/196, 210, 251, 420
		h	2945	—	193/194/195/196, 210, 251, 420
XV	1190	i	3187	3196	127, 197, 211, 253, 323, 393, 462
		j	3400	3396	127, 197, 211, 239, 281, 351, 421, 491

^*See Fig. 1. 

^†As determined by APCI/MS mass spectra. 

^‡See ref. 25 for details. 

^§Identified by authentic standard. 

^¶ No retention indices can be calculated due to lack of data on retention shifts by cyclopentyl moieties. However, the later elution time of carbon skeleton h compared to carbon skeleton f is in agreement with the later elution time of carbon skeleton c compared to carbon skeleton a.