MS - Ionization techniques

Question 1

Electron ionization (EI)

Answer 1

Volatile

1. Volatile compound bombarded with e-
2. e- knock e- of atoms away
3. atoms become +
4. repelled

Lot of fragmentation

Question 2

Chemical ionization (CI)

Answer 2

Volatile

1. Reagent gas hit with e- –> becomes reagent ion
2. Reagent ion reacts with analyte –> analyte becomes ionized (proton / hydride transfer)

Higher abundance pseudomolecular ions
High mass fragments (bc less fragmentation)
Simple spectra
Choice reagent gass determines degree of fragmentation

Question 3

MALDI

Answer 3

Non-volatile

1. Sample dissolved in matrix (aromatic compounds)
2. Matrix hit with laser –> matrix ionized + gas phase
3. Charge slowly transferred to sample –> sample becomes ionized

Optimal matrix for each compound
Lower mass region spectrum = matrix
Not absolutely quantative

Question 4

Electrospray

Answer 4

Non-volatile

1. High voltage on needle –> analyte ionized
2. Droplets exit needle
3. Desolvation of analyte
4. Detection

Analytes can have more than +1 charge
Solvent has to evaporate quickly

Question 5

Nanoflow

Answer 5

Small ESI
Low sample consumption
Less contamination MS
More tolerant to salts, buffers, detergents