Positive and negative ion mode
Lipid classes Type of overlap Example PE O – LPE PE O = LPE [PE O-26:1+H] + = [LPE 26:1+H] + PC O – LPC PC O = LPC [PC O-26:1+H] + = [LPC 26:1+H] + DB = Double Bond Positive ion mode
Lipid classes Type of overlap Example PC-PE PC = PE + 3CH 2 [PC 32:0+H] + = [PE 35:0+H] +[PC 32:0+Na] + = [PE 35:0+Na] + PC-PA [PC+H] + = [PA+5CH 2+DB+NH 4] + [PC 32:0+H] + = [PA 37:1+NH 4] + PE-PA [PE+H] + =[PA+C 2H 4+DB+NH 4] + [PE 34:1+H] + = [PA 36:2+NH 4] + PS-PG [PS+H] + = [PG+2DB+NH 4] + [PS 34:1+H] + = [PG 34:2+NH 4] + SM – CerPE SM = CerPE + 3CH 2 [SM d34:1+H] + = [CerPE d37:1+H] + DB = Double Bond Negative ion mode
Lipid classes Type of overlap Example PC-PS* [PC+HCOO] – = [PS+3CH 2-DB-H] – [PC 33:1+HCOO] – = [PS 36:0-H] – PC-PS [PC+CH 3CO 2] – = [PS+4CH 2-DB-H] – [PC 32:1+CH 3COO] – = [PS 36:0-H] – all lipid classes forming acetate/formate adducts* [X+CH 2+HCOO] – = [X+CH 3COO] – [PC 34:1+HCOO] – = [PC 33:1+CH 3COO] –[Cer d35:1+HCOO] – = [Cer d34:1+CH 3COO] – DB = Double Bond
*Acetate salts of LC-MS grade can be contaminated with trace amounts of formate, which can lead to false-positive identification. Methanol can be oxidized to formic acid during electrospray ionization.