. 2017 Aug 3;12(8):e0182423. doi: 10.1371/journal.pone.0182423

Table 1. Conditions for the regiochemical assignment of fatty acids at sn-1, sn-2 and sn-3 positions in glycerolipids.

Analyzed lipids	Parental ion to be fragmented	MS2 fragments properties	References
Phospholipids
phosphatidylcholines (PC)	[M+H]⁺	[M+H-R₂CH = C = O]⁺>[M+H-R₁CH = C = O]⁺	[31]
Phosphatidylethanolamines (PE)	[M-H]^-	[R₂COO]^->[R₁COO]^-	[32]
phosphatidylglycerols (PG)	[M-H]^-	[M-H-R₂COOH]^->[M-H-R₁COOH]^-	[33]
phosphatidylinositols (PI)	[M-H]^-	[M-H-R₂COOH]^->[M-H-R₁COOH]^-	[34]
Phosphatidic acids (PA)	[M-H]^-	[M-H-R₂COOH]^->[M-H-R₁COOH]^-	[35]
Cardiolipins (DPG)	[M-H]^-	MS2 produced the corresponding PA	[36]
Non phosphorus glycerolipids
sulfoquinovosyldiacylglycerols (SQDG)	[M-H]^-	[M-H-R₁COOH]^->[M-H-R₂COOH]^-	[37]
Monogalactosyldiacylglycerols (MGDG)	[M+Na]⁺	[M+Na-R₁COO^-]⁺>[M+Na-R₂COO^-]⁺	[38]
digalactosyldiacylglycerols (DGDG)	[M+Na]⁺	[M+Na-R₁COO^-]⁺>[M+Na -R₂COO^-]⁺	[38]
diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-β-alanine (DGTA)	[M+H]⁺	[M+H-R₂COOH]⁺>[M+H-R₁COOH]⁺	By analogy with phospholipid diacylglycerol moiety
diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-homoserine (DGTS)	[M+H]⁺	[M+H-R₂COOH]⁺>[M+H-R₁COOH]⁺ Can be differentiated from DGTA by a neutral loss of m/z 87	By analogy with phospholipid diacylglycerol moiety
Neutral lipids
Diacylglycerol (DAG)	[M+NH₄]⁺	[M+NH₄-R₁COONH₄]⁺>[M+NH₄-R₂COONH₄]⁺	[39]
Triacylglycerol (TAG)	[M+NH₄]⁺	[M+NH₄-R_1/3COO^-]⁺>[M+ NH₄-R₂COO^-]⁺	[40]