34
2 Summary Tables
2.5.7 Indicators of the Presence of Heteroatoms
In low-resolution mass spectra, one often observes characteristic isotope patterns,
specific masses of fragment ions, and characteristic mass differences (Δm) between
the molecular ion (M +· ) and fragment ions (frag + ) or between fragment ions. High
resolution mass spectra can be used to confirm the elemental composition provided
that the resolution is sufficient to discriminate alternative compositions. Moreover,
tandem mass spectrometry (also called MS/MS) may be used to identify characteristic losses of heteroatoms from parent or fragment ions.
Indication of O: Δm 17 from M +· , in N-free compounds
Δm 18 from M +·
Δm 18 from frag + , particularly in aliphatic compounds
Δm 28, 29 from M +· for aromatic compounds
Δm 28 from frag + for aromatic compounds
m/z 15, relatively abundant
m/z 19
m/z 31, 45, 59, 73, … + (14) n
m/z 32, 46, 60, 74, … + (14) n
m/z 33, 47, 61, 75, … + (14) n for 2 × O, in the absence of S
m/z 69 for aromatic compounds meta-disubstituted by O
Indication of N: M +· odd-numbered (indicates odd number of N in M +· )
Large number of even-numbered fragment ions
Δm 17 from M +· or frag + , in O-free compounds
Δm 27 from M +· or frag + , for aromatic compounds or nitriles
Δm 30, 46 for nitro compounds
m/z 30, 44, 58, 72, … + (14) n for aliphatic compounds
Indication of S: Isotope peak [M+2] +· ≥ 5% of M +·
Δm 33, 34, 47, 48, 64, 65 from M +·
Δm 34, 48, 64 from frag +
m/z 33, 34, 35
m/z 45 in O-free compounds
m/z 47, 61, 75, 89, … + (14) n unless compound with 2 × O
m/z 48, 64 for S-oxides
Indication of F: Δm 19, 20, 50 from M +·
Δm 20 from frag +
m/z 20
m/z 57 without m/z 55 in aromatics
2 Summary Tables
2.5.7 Indicators of the Presence of Heteroatoms
In low-resolution mass spectra, one often observes characteristic isotope patterns,
specific masses of fragment ions, and characteristic mass differences (Δm) between
the molecular ion (M +· ) and fragment ions (frag + ) or between fragment ions. High
resolution mass spectra can be used to confirm the elemental composition provided
that the resolution is sufficient to discriminate alternative compositions. Moreover,
tandem mass spectrometry (also called MS/MS) may be used to identify characteristic losses of heteroatoms from parent or fragment ions.
Indication of O: Δm 17 from M +· , in N-free compounds
Δm 18 from M +·
Δm 18 from frag + , particularly in aliphatic compounds
Δm 28, 29 from M +· for aromatic compounds
Δm 28 from frag + for aromatic compounds
m/z 15, relatively abundant
m/z 19
m/z 31, 45, 59, 73, … + (14) n
m/z 32, 46, 60, 74, … + (14) n
m/z 33, 47, 61, 75, … + (14) n for 2 × O, in the absence of S
m/z 69 for aromatic compounds meta-disubstituted by O
Indication of N: M +· odd-numbered (indicates odd number of N in M +· )
Large number of even-numbered fragment ions
Δm 17 from M +· or frag + , in O-free compounds
Δm 27 from M +· or frag + , for aromatic compounds or nitriles
Δm 30, 46 for nitro compounds
m/z 30, 44, 58, 72, … + (14) n for aliphatic compounds
Indication of S: Isotope peak [M+2] +· ≥ 5% of M +·
Δm 33, 34, 47, 48, 64, 65 from M +·
Δm 34, 48, 64 from frag +
m/z 33, 34, 35
m/z 45 in O-free compounds
m/z 47, 61, 75, 89, … + (14) n unless compound with 2 × O
m/z 48, 64 for S-oxides
Indication of F: Δm 19, 20, 50 from M +·
Δm 20 from frag +
m/z 20
m/z 57 without m/z 55 in aromatics