Transcript Lecture 14 - Oct 29 - University of Toronto

Lecture 14
LC-MS
Ionization
GC-MS
GC
MS
Computer
LC-MS
LC
MS
Computer
MS Analysis
MS
Gas phase
Ions
H3CH2CH2C
CH2CH2CH3
O2N
NO2
LC?
CF3
OH
F
F
F
F
O
S
F F
F O
O
Condensed Phase Ionization
Electrospray Ionization (ESI)
Atmospheric Pressure Chemical Ionization (APCI)
Atmospheric Pressure Photoionization (APPI)
Matrix Assisted Laser Desorption/Ionization (MALDI)
Desorption Electrospray Ionization (DESI)
Direct Analysis in Real Time (DART)
Liquid
phase
(LC)
Solid
phase
PCBs
Production
started
1920s
Env Detection
1968
Difference?
PFOS
Production
started
1930s
Env Detection
2001
MS Analysis
GC-MS and LC-MS ionization are very different
GC – Producing ions from gas phase analytes
LC – Producing gas phase compounds from charged
analytes
Necessary for certain important analytes:
– Biological molecules:
• Proteins
• Amino acids/nucleic acids
• sugars
– Strong acids without the ability to absorption UV-vis
Problem solved…
Electrospray Ionization
(ESI)
John Fenn
Electrospray Ionization
(ESI)
ESI Key Features:
LC
- Capillary (LC) 90o to Cone (MS)
- Atmospheric pressure ion source
Ionization
Chamber
Capillary
- Heat applied to evaporate solvent
Gas
+
Heater
MS
10-6 torr
Sample
Cone
Nebulized
Spray
- Nebulized flow through capillary
- Voltage difference applied
between capillary and cone
- Detect (+) ions  Cap (+), Cone (-)
- Detect (-) ions  Cap (-), Cone (+)
What happens in the droplet?
760 torr
Electrospray Ionization
(ESI)
+ ++
+ ++
P. Kebarle, J. Mass Spectrom. 2000, 35, 804–817.
Interested in Positive Ions
- Apply (+) Voltage to capillary
- (+) ions repelled from capillary
- (-) ions attracted to capillary
- Results in droplets enriched in
(+) ions
Electrospray Ionization
(ESI)
Summary
– Ions are formed in condensed phase
• In mobile phase droplets
– Ions move into the gas phase by two mechanisms:
• Partition into gas phase due to columbic repulsion in droplet
• Solvent in droplet evaporates leaving ion behind
Works well for compounds that can
be charged in the condensed phase
Strong or weak
Acids and Bases
F
F
F
F
CH2CH2CH3
O2N
NO2
O
S
F F
H3CH2CH2C
F O
O
OH
CF3
Atmospheric Pressure Chemical Ionization
(APCI)
APCI Key Features:
LC
- Capillary (LC) 90o to Cone (MS)
- Atmospheric pressure ion source
- Nebulized flow through capillary
Ionization
Chamber
Capillary
- No voltage applied to capillary
- droplets are not charged
Gas
Heater
MS
10-6 torr
Sample
Cone
Nebulized
Spray
- Heat applied to evaporate solvent
Corona
discharge
needle
760 torr
- Voltage still applied to cone
- Detect (-) ions  Cone (+)
- Detect (+) ions Cone (-)
- Heat evaporates solvent, analytes
partition into the gas-phase
uncharged
- Need to make ions!
Atmospheric Pressure Chemical Ionization
(APCI)
Summary
– First step is solvent evaporation
• Compounds in gas-phase as neutrals
– Ions produced in the gas-phase
• Corona discharge ionizes carrier gas and mobile phase
• Acid/base reactions in the gas phase with mobile phase
F
F
F
F
O
S
F F
F O
Works well for compounds that are protic
but neutral at a pH between 2 and 9
Weak
Acids / Bases
H3CH2CH2C
CH2CH2CH3
O2N
NO2
O
OH
CF3
Atmospheric Pressure Photoionization
(APPI)
APPI Key Features (same as APCI):
LC
- Capillary (LC) 90o to Cone (MS)
- Atmospheric pressure ion source
- Nebulized flow through capillary
Ionization
Chamber
Capillary
- No voltage applied to capillary
- droplets are not charged
Gas
Heater
MS
UV
lamp
10-6 torr
Sample
Cone
Nebulized
Spray
- Heat applied to evaporate solvent
760 torr
- Voltage still applied to cone
- Detect (-) ions  Cone (+)
- Detect (+) ions Cone (-)
- Heat evaporates solvent, analytes
partition into the gas-phase
uncharged
- Need to make ions!
Atmospheric Pressure Photoionization
(APPI)
Summary
– First step is solvent evaporation
• Compounds in gas-phase as neutrals
– Ions produced in the gas-phase
•
•
•
•
F
F
F
F
UV lamp ionizes compound by photon absorption or
Charge exchange with dopant or
Dopant ionizes mobile phase, followed by;
Acid/base reactions in the gas phase with mobile phase
O
S
F F
Works well for compounds that are absorb UV radiation or
are protic but neutral at a pH between 2 and 9
Weak Acids / Bases
H3CH2CH2C
CH2CH2CH3
Nonpolar compounds that are UV active
O2N
O
NO2
F O
OH
CF3
Summary LC-MS Ionization
m/z
(MW)
www.agilent.com
Matrix-Assisted Laser
Desorption/Ionization (MALDI)
MS
MALDI Key Features:
Vacuum
+
-
+
Laser beam
- Analyte deposited on surface with
excess matrix compound
- Shine laser on the surface
- hn aborbed by matrix molecules
- Matrix molecules transfer energy
to analyte molecules
- Results in desorption/ionization of
both matrix and analyte
Analyte molecule
Matrix molecule
Adapted from Dass, C. Fundamentals of Contemporary Mass Spectrometry, Wiley-Interscience, 2007.
Matrix-Assisted Laser
Desorption/Ionization (MALDI)
Common dopants:
O
HO
H
C
COOH
C
C
C
OH
OH
HO
N
Analytes of interest:
– Proteins
– Polymers
– High MW, ionization not possible using ESI,
APCI, APPI
– High MW separates these compounds from the
background signal of the matrix
Desorption Electrospray Ionization
(DESI)
Z. Takáts et al. Science 2004, 306, 471-473.
Direct Analysis in Real Time
(DART)