HP Data Explorer 4 Isotopic pattern in mass spectra

Isotopes

As the number of carbon atoms in a compound increases, the possibility of the compound containing a 13C instead of a 12C also increases. A compound with ten carbon atoms includes a molecular ion M+ and an isotopic ion (M+1)+ one mass unit greater than the molecular ion, which is approximately

11 percent of the abundance of the molecular ion. The possibility of including two 13C atoms in the same molecule also increases with increasing number of carbon atoms. Therefore, (M+2)+ ions become more visible. In a compound with ten carbon atoms such as decahydro naphthalene,

C10H18 (Figure B-2), relative heights of M+, (M+1)+, and (M+2)+ B peaks are 100:11:0.5.

M+

(M+1)+

(M+2)+

Isotopic pattern in mass spectra

Figure B-2 Mass Spectrum of Decahydro Naphthalene

All compounds containing carbon include molecular ions and isotopic ions that are 1 and 2 mass units higher than the molecular ion. At higher masses, the isotopic pattern of a mass spectrum is more pronounced as the relative abundance of isotopes increases. In angiotensin I (Figure B-3)with a molecular weight of 1,296 Da, (C62H89O14N17), a peak containing one 13C isotope is approximately 70 percent of the pure 12C peak.

Data Explorer™ Software User’s Guide B-3