Thomas Michel

Question 1

Basic Prin. of MS

Answer 1

generate ions, suitable method, seperate m/z, qualitative, quantitative, abundance

Question 2

EI (Electron impact inonization)

Answer 2

70 eV, for volatile organic mol., fragment

Question 3

CI (Chemical ionization)

Answer 3

Collision with primary ions, little excess E, less fragment, pseudo M+H ion, proton transfer, electropholic addition, anion abstraction, charge exchange; Gas (methane, isobutane, ammonia); + & -

Question 4

Thermalspray

Answer 4

1983, vacuum chamber, supersonic beam, repeller

Question 5

ESI (Electrospray ionization)

Answer 5

Protein, small polar mol., high sen., easy to couple with LC and capillary electrophoresis
[Talor cone, capillary & counter electrode (3-6 kV)
Capillary flow (1-10 microL/min)]
+ NH4, Na, K, OAc, Cl
Avoid (nonpolar sample, buffer

Question 6

APCI (Atmospheric Pressure Chemical Inonization)

Answer 6

Spray Heated (250-400); Corona needle = solvent ionized; transfer charge -> MH+
Ion suppression not so important
Sensitive at high flow rate than ESI
Non polar solvent not good for ESI is OK for APCI
Avoid: Sample thermally labile, polar & high mwt compound (because vaporation process)

Question 7

APPI (Atmospheric pressure photoionization)

Answer 7

Photons, 2000, nebulization gas (N2) heat to 250-500 oC, discharge lamp
[Best lamp (Kr = 10->10.6 eV)]
Doping solvent (/^ 10-100 times sensitivity; Toluene, acetone, methanol,...)
Direct Photoionization, proton transfer, charge exchange.
M.+ and MH+

Question 8

ESI vs APCI/APPI

Answer 8

ESI:Volatility not required; polar, high mwt, thermal labile; Ions form in solution; cam form multiply charge
APCI/APPI: Volatility required; must be thermally stable; Ions form in gas phase; Singly charge only.

Question 9

FAB (Fast atom bombardement)

Answer 9

Known as liquid secondary ion mass spectrometry (LSIMS); 1980; large biological mol. 300

Question 10

MALDI (Matrix Assisted Laser Desorption Ionization)

Answer 10

Sample Mix in a large quanlity of matrix, deposit onto surface (metal plate)
Laser irradiation
Desorption MH+, M+Cat+, M-H-

Question 11

DESI (Desorption ESI)

Answer 11

soft, +&-, multiply charged
No matrix; peptides, proteins, pharmaceutical, natural pro. polymers,...
Solvent spray (like ESI) to sample surface (atmospheric, freely move), secondary ions form after sample desorption.

Question 12

DART (direct analysis in real time)

Answer 12

Generate ions from neutral and metastable atoms;
No sample preparation
Non-contact sample surface;
Not affected by humidity
Cross section? 100A
MH+ and M- or M-H-
Single charge only; No Na K adduct
Unaffected by choice of solvents
No need to dissolution or chromatography

Question 13

Key factor to choice ionization mode:

Answer 13

depend on compound nature:
Solubility
Polarity
Volatility
Thermal Stability
Molecular Mass