. Author manuscript; available in PMC: 2021 Aug 5.

Published in final edited form as: Anal Chem. 2019 Dec 17;92(1):1386–1394. doi: 10.1021/acs.analchem.9b04542

Table 1.

Tentative SI identifications.

SIMS m/z	Tentative ID	Tentative Chemical Formula	Reference	MALDI FT-ICR MS error (ppm)	Region (sub-layer)	Ion form	Symbol
134.1	Adenine	C₅H₄N₄^-	SIMS ⁵¹		Epidermis (SG,SS)	[M-H]-	•
168.0	SM Headgroup	C₄H₁₁NO₄P^-	SIMS ⁵²		Dermis	-	○
253.2	FA 16:1	C₁₆H₂₉O₂^-	SIMS ^{18–20, 53} LC-MS ²²		Dermis, Epidermis	[M-H]-	▲
255.2	FA 16:0	C₁₆H₃₁O₂^-	SIMS ^{18–20, 53} LC-MS ²²		Dermis, Epidermis	[M-H]-	▲
279.2	FA 18:2	C₁₈H₃₁O₂^-	SIMS ^{18–20, 53} LC-MS ²²		Dermis, Epidermis	[M-H]-	▲
281.2	FA 18:1	C₁₈H₃₃O₂^-	SIMS ^{18–20, 53} LC-MS ²²		Dermis, Epidermis	[M-H]-	▲
283.3	FA 18:0	C₁₈H₃₅O₂^-	SIMS ^{18–20, 53} LC-MS ²²		Dermis, Epidermis	[M-H]-	▲
311.3	FA 20:0	C₂₀H₃₉O₂^-	LC-MS ²²		Epidermis (SC)	[M-H]-	▼
325.3	FA 21:0	C₂₁H₄₁O₂^-	SIMS ²⁰ LC-MS ²²		Epidermis (SC)	[M-H]-	▼
339.3	FA 22:0	C₂₂H₄₃O₂^-	SIMS ^{20, 53} LC-MS ²²		Epidermis (SC)	[M-H]-	▼
353.3	FA 23:0	C₂₃H₄₅O₂^-	SIMS ^{20, 53} LC-MS ²²		Epidermis (SC)	[M-H]-	▼
367.4	FA 24:0^*	C₂₄H₄₇O₂^-	SIMS ^{20, 36, 53} LC-MS ²²	0.81	Epidermis (SC)	[M-H]-	▼
381.4	FA 25:0	C₂₅H₄₉O₂^-	SIMS ^{20, 53} LC-MS ²²		Epidermis (SC)	[M-H]-	▼
395.4	FA 26:0^*	C₂₆H₅₁O₂^-	SIMS ^{20, 36, 53} LC-MS ²²	−1.42	Epidermis (SC)	[M-H]-	▼
409.4	FA 27:0	C₂₇H₅₃O₂^-	SIMS ²⁰ LC-MS ²²		Epidermis (SC)	[M-H]-	▼
426.4	FA 28:0	C₂₈H₅₅O₂^-	SIMS ²⁰ LC-MS ²²		Epidermis (SC)	[M-H]-	▼
429.4	α-Tocopherol	C₂₉H₄₉O₂^-	SIMS ²⁰		Dermis	[M-H]-	■
465.3	Cholesterol sulfate^**	C₂₇H₄₅SO₄^-	SIMS ^{20, 36, 53}	0.53	Epidermis (SS,SG,SC)	[M-H]-	♦

Lipids denoted with a * were confirmed by complimentary MALDI FT-ICR MS analysis.

Cholesterol sulfate (**) was additionally confirmed using MS².