Mass Spectrometry (Ionization)

Question 1

Hard Ionisation (Definition)

Answer 1

High in energy, lots of fragmentation and not good for mixtures

Question 2

Soft Ionisation (Definition)

Answer 2

Low energy, minimises fragmentation so there is a simpler molecular spectrum, identifies parent mass

Question 3

Hard Ionisation (Examples)

Answer 3

Electron Impact Ionisation (EI)

Question 4

Soft Ionisation (Examples)

Answer 4

Resonant two-photon ionisation (R2PI)
Chemical Ionization (CI) reagent gas ion, PTR-MS, MALDI, ESI,

Question 5

CI (Defintion)

Answer 5

Ionization source chamber filled with a reagent gas, where energetic electrons ionise gas

Question 6

CI (Formation of reagent ions)

Answer 6

Step 1: CH4 + e- -> CH4+ + 2e-
Step 2: CH4 + CH+ -> CH5+
CH3+ + CH4 -> C2H5+ + H2

Question 7

CI (Psuedomolecular ions)

Answer 7

CH5+ + M -> CH4 + MH+

Question 8

CI (Adduct ions)

Answer 8

C2H5+ + M -> [M+C2H5]+ (M+29)

Question 9

CI (Molecular ion by charge transfer)

Answer 9

CH4+ + M -> M+ + CH4

Question 10

CI (Hydride abstraction)

Answer 10

C3H5+ + M -> C3H6 + [M-H]+

Question 11

PT-MS (Defintion)

Answer 11

Soft Ionisation: R + H3O+ -> RH+ + H2O

Generates protonated parent ion in mass spec
Only ionises species with species of proton affinity > H2O