Isobaric Overlap
Positive and negative ion mode
Lipid classes | Type of overlap | ∆m/z | Examples |
DB containing classes | [M+DB+13C2] ≈ [M] **Overlap resulting from natural 13C abundance of 1.1% was selected as prevailing overlap; other isotopes like two deuterium or 18O may lead to similar isobaric overlaps. | 0.009 | [PC 32:1+H+13C2]+ ≈ [PC 32:0+H]+ |
Glycerolipids | [M] ≈ [M+CH2+O] | 0.036 | [PC 33:1+H]+ ≈ [PC O-34:1+H]+ |
Sphingolipids | [M] ≈ [M+CH2-DB-OH] | 0.036 | [SM t42:2] ≈ [SM d43:1] |
PI – PS | [PI] ≈ [PS+6CH2+5DB+13C] | 0.002 | [PI 34:1-H]– ≈ [PS 40:6-H+13C]– |
PC – SM | [PC+13C] ≈ [SM-OH2 +4CH2-DB] | 0.065 | [PC 38:3+13C] ≈ [SM d42:2] |
Positive ion mode
Lipid classes | Type of overlap | ∆m/z | Examples |
DB containing classes | [M+Na]+ ≈ [M+2CH2+3DB+H]+ | 0.002 | [PC 34:1+Na]+ ≈ [PC 36:4+H]+ |
PC – PS | [PC+H]+ ≈ [PS+DB+H]+ | 0.073 | [PC 32:0+H]+ ≈ [PS 32:1+H]+ |
DG – CE | [CE X:Y+NH4]+ ≈ [DG X+30:Y+NH4]+ | 0.015 | [CE 18:1+NH4]+ ≈ [DG 38:1+NH4]+ |
Negative ion mode
Lipid classes | Type of overlap | ∆m/z | Examples |
DB containing classes | [M+35Cl]– ≈ [M+DB+37Cl]– | 0.019 | [PC 34:1+35Cl]– ≈ [PC 34:2+37Cl]– |
PA – CL2- | [PA X:Y-H]– ≈ [CL 2X:2Y-2H]2- | 0.018 | [PA 34:2-H]– ≈ [CL 64:4-2H]2- |
Isobaric fragment ions
Lipid classes | Type of overlap | ∆m/z | Examples |
FA fragments | FA X:Y(+O) ≈ FA X+4:Y+6(-CO) | 0.021 | [FA 18:0-H]– ≈ [FA 22:6-H-CO2]– |
FA fragments | FA X:Y(+O) ≈ FA X+3:Y-1(-CO) | 0.073 | [FA 20:4-H]– ≈ [FA 23:3-H-CO2]– |