ionization in order to obtain intact molecular ions, that can be separated. Then
selected ions can be transferred to the second mass analyzer for a second measurement. Prior to this second separation a hard ionization induces fragmention forming
fragment ions (so-called daughter ions) from the isolated molecular ion. This process
enables a first isolation of a substance by the molecular ion and, subsequently, the
detection of structural information by corresponding fragments. This approach
compound name
elemental
formula
molecular
structure
nominal
mass
excact
mass
heptane
C 7 H 16
100
100.125
hexanone
C 6 H 12 O
100
100.089
∂-valerolactone
C 5 H 8 O 2
100
100.052
thiocyclopentanone
C 5 H 8 S
100
100.035
O
O
O
S
-36 mmu
-33 mmu
-17 mmu
Fig. 4.29 Illustration on how exact mass spectrometry enables to obtain information on elemental
composition of measured signals
sample
A, B, C ….
A +
B +
C +
B +
sof t ionisaƟon
B + - Z
B + - Y
B + - X
B +
B +
mass spectrum of the mixture
mass spectrum of daugther
ions of the component B
mulƟ-component
mixture
hard ionisaƟon
daugther ions
C +
A +
Fig. 4.30 Scheme of a MSxMS device and the type of measurement (modified after Cammann
2010)
70
4 Instrumental Analysis