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With examples explain how small M+1 and M+2 peaks may be seen or appear in mass spectral.
Accepted Answer
M+1 and M+2 Peaks in Mass Spectrometry
M+1 Peak:
Origin: The presence of a small amount of the 13C isotope in a molecule.
Explanation: Carbon-13 is a naturally occurring stable isotope of carbon, present in about 1.1% abundance. When a molecule containing carbon is ionized, a small fraction of the ions will contain 13C instead of the more abundant 12C. This results in a peak one mass unit higher than the molecular ion peak (M+).
Example: Consider a molecule with the molecular formula CH4. The M+ peak would be at m/z 16, corresponding to the 12C1H4 ion. The M+1 peak at m/z 17 would be due to the 13C1H4 ion.
M+2 Peak:
Origin: Presence of heavier isotopes like 2H (deuterium), 18O, or 35Cl in the molecule.
Explanation: The M+2 peak arises from the presence of heavier isotopes in the molecule. The abundance of these isotopes is typically lower than 13C, leading to smaller M+2 peaks.
Examples:
Chlorine: Chlorine has two isotopes, 35Cl (75.77%) and 37Cl (24.23%). If a molecule contains chlorine, its mass spectrum will show an M+2 peak about 3% of the intensity of the molecular ion peak.
Bromine: Bromine has isotopes 79Br (50.69%) and 81Br (49.31%). The M+2 peak is about the same intensity as the molecular ion peak due to the near-equal abundance of the two isotopes.
Oxygen: Oxygen-18 is present in a small amount (~0.2%) in nature. Molecules containing oxygen can show a small M+2 peak due to the presence of 18O.
Note: The relative intensity of M+1 and M+2 peaks can provide information about the number of carbon atoms, chlorine atoms, and other elements present in a molecule.
M+1 Peak:
Origin: The presence of a small amount of the 13C isotope in a molecule.
Explanation: Carbon-13 is a naturally occurring stable isotope of carbon, present in about 1.1% abundance. When a molecule containing carbon is ionized, a small fraction of the ions will contain 13C instead of the more abundant 12C. This results in a peak one mass unit higher than the molecular ion peak (M+).
Example: Consider a molecule with the molecular formula CH4. The M+ peak would be at m/z 16, corresponding to the 12C1H4 ion. The M+1 peak at m/z 17 would be due to the 13C1H4 ion.
M+2 Peak:
Origin: Presence of heavier isotopes like 2H (deuterium), 18O, or 35Cl in the molecule.
Explanation: The M+2 peak arises from the presence of heavier isotopes in the molecule. The abundance of these isotopes is typically lower than 13C, leading to smaller M+2 peaks.
Examples:
Chlorine: Chlorine has two isotopes, 35Cl (75.77%) and 37Cl (24.23%). If a molecule contains chlorine, its mass spectrum will show an M+2 peak about 3% of the intensity of the molecular ion peak.
Bromine: Bromine has isotopes 79Br (50.69%) and 81Br (49.31%). The M+2 peak is about the same intensity as the molecular ion peak due to the near-equal abundance of the two isotopes.
Oxygen: Oxygen-18 is present in a small amount (~0.2%) in nature. Molecules containing oxygen can show a small M+2 peak due to the presence of 18O.
Note: The relative intensity of M+1 and M+2 peaks can provide information about the number of carbon atoms, chlorine atoms, and other elements present in a molecule.
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