Applied Biosystems Data Explorer 4 Series User Manual page 391

Isotopic pattern
in mass spectra
As the number of carbon atoms in a compound increases, the
possibility of the compound containing a
also increases. A compound with ten carbon atoms includes a
+
molecular ion M and an isotopic ion (M+1)
greater than the molecular ion, which is approximately
11 percent of the abundance of the molecular ion. The
possibility of including two
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,
C H (Figure B-2), relative heights of M
10 18
peaks are 100:11:0.5.
+
M
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, (C
13
containing one C isotope is approximately 70 percent of the
12
pure C peak.
Data Explorer
13
C instead of a
+
one mass unit
13
C atoms in the same molecule
+
, (M+1)
+
(M+1)
(M+2)
H O N ), a peak
62 89 14 17
™
Software User's Guide
Isotopes
12
C
B
+ +
, and (M+2)
+
B-3