Mass Spectrometry Flashcards
What happens to the compound in the ionization chamber of a mass spectrometer?
The compound is vaporized and bombarded with fast-moving electrons, which knock out electrons from the molecules, converting them into molecular ions.
Write the ionization reaction for ethanol (CH₃CH₂OH).
CH₃CH₂OH + e⁻ → CH₃CH₂OH⁺ (molecular ion) + 2e⁻
What causes molecular ions to break into smaller fragments?
Molecular ions are unstable and break up into smaller ions called fragments.
How are the positive fragments detected in a mass spectrometer?
The positive fragments are attracted to negatively charged electrodes, pass through an opening, and are exposed to a magnetic field that deflects them based on their mass-to-charge (m/z) ratio.
What determines the degree of deflection of ions in a mass spectrometer?
The mass-to-charge ratio (m/z) of the ions determines their deflection.
List some likely fragments and their mass-to-charge values.
CH₃⁺ = 15
CH₃CH₂⁺ = 29
CH₂OH⁺ = 31
C₃H₇⁺ = 43
COOH⁺ = 45
C₆H₅⁺ = 77
What is the significance of the M+1 peak in mass spectrometry?
The M+1 peak indicates the presence of C-13 isotopes, which constitute 1.1% of all carbon atoms. It helps calculate the number of carbon atoms in a compound.
How do you calculate the number of carbon atoms in a compound using M and M+1 peaks?
100 x (abundance of M+1/ abundance of M)
Explain the presence of multiple lines in the mass spectrum of NCl₃.
The multiple lines are due to particles containing nitrogen and chlorine isotopes (Cl-35 and Cl-37), leading to fragments with different mass-to-charge values.
