mass spectra Flashcards
Typical peaks in the EI mass spectra of n-alkanes are 41, 55, 69. Molecular peak has typically a high intensity.
no: m/z = 29, 43, 57, 71; low intensity
EI mass spectra of alkylated monocyclic aromatic hydrocarbons are characterized by the presence of a peak with m/z 91, which corresponds to the tropylium cation.
yes
The molecular ion is always present in EI mass spectra.
no
The EI mass spectra of polycyclic aromatic hydrocarbons (PAHs) are characterized by a doubly charged molecular ion (z=2), which has an m/z value two units lower than the singly charged molecular ion.
no, Doubly charged ions are rare in EI and, if present, their
m/z values would be approximately half those of singly charged ions, not “two units lower.”
Cycloalkanes display similar EI mass spectra patterns as alkenes.
yes
N-alkanes and i-alkanes have the same practically indistinguishable EI mass spectra.
no
Polycyclic aromatic hydrocarbons (PAHs) usually give richly fragmented EI mass spectra. A molecular ion is usually of very low intensity.
true
Mass spectra are used to determine the molecular weight of a compound.
yes
The molecular formula of the characteristic fragments in the EI mass spectra of n-alkanes is CnH2n+1.
yes
In mass spectra, the highest peak is referred to as the base peak. This peak always represents the molecular ion.
no
Do Isotopes differ in the total number of neutrons?
yes
Mass spectra are used to determine the structure of a compound
yes
In MS, cold reservoir prevents evaporation before ionization
yes
what is API?
atmospheric pressure ionization)
Ionization of the analyte occurs either under vacuum or under atmospheric pressure
true
Based on what ionization techniques are divided into2 groups: hard and soft?
based on the energy that is transferred to the analyte during the ionization process
Is electron ionization considered to be hard ionization?
yes
Is electron ionization the only example of hard ionization?
yes
What info is given about a compound during hard ionization?
1) structure of the analyte
2) molecular weight
3) molecular weight distribution
1) structure
What info is given about a compound while performing soft ionization?
1) structure
2) molecular weight
2) molecular weight