polaris q gc/ms n ion trap technology
DESCRIPTION
Polaris Q GC/MS n Ion Trap Technology. Steven T. Fannin. GC & GC/MS. The Column: “heart” of the Instrument. Maintaining GC/MS Ruggedness. “Extra Column” Effects Syringes Septa Liners Ferrules Gas Filters. Chromatography: General Overview. Resolution Selectivity - PowerPoint PPT PresentationTRANSCRIPT
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Polaris Q GC/MSn Ion Trap Technology
Steven T. Fannin
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GC & GC/MS
The Column: “heart” of the Instrument
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Maintaining GC/MS Ruggedness
“Extra Column” Effects
• Syringes
• Septa
• Liners
• Ferrules
• Gas Filters
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Chromatography: General Overview
H = A + B/u + C u
• Resolution
• Selectivity– Spacing between two peaks
– Important role in GC confirmation analyses
• Capacity Factor (Relative Retention)– Retention relative to an unretained
compound
• Column Efficiency:
The Van Deemter equation: H = A + B/u + C u A: the multipath term (eddy diffusion)B: longitudinal diffusionC: resistance to mass transfer
Why Capillary Columns?
H = L/N
N.B: Velocity: Pressure regulated vs Flow controlled
H2 vs He vs N2
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Common Mass Analyzers for GC/MS
• Time of Flight (TOF) - Ionized compounds/fragments from the source are directed into a flight tube. Ions are separated by virtue of their different flight times over a known distance.
• Magnetic Sector - Uses a combination of magnetic and electrical fields to sort ions. The ions are focused and resolved by passing through an electric field then a magnetic field.
• Quadrupole - consists of two sets on opposing rods. This mass analyzer uses a combination of RF and DC modulation to sort ions.
• Ion Trap - operates on a principle as the quadrupole; however ions can be stored for subsequent analysis. The ions are sorted by changing the electric field inside of the trap by manipulating the RF field and sequentially ejecting the ions from low to high mass to charge.
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General Mass Spectrometry CharacteristicsWhat differentiates mass analyzers is how they perform mass analysis
• Mass Analysis - Common to Mass Analyzers– All determine the m/z ratio
– All measure gas-phase ions
– All operate at low pressure (<10-4 Torr) to allow appropriate mean free path of gas phase ions
• General Mass Spectrometry Instrument Characteristics– Sensitivity
– Tandem Mass Spectrometry
– Mass Range
– Resolution
– Mass Accuracy
– Scan Speed
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GC/MS Ionization Methods
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Electron Ionization: EI (“Hard Ionization”)
• Transfer of energy to a neutral molecule (in the gaseous state) to eject one of its own electrons and produce an ion (charged molecule), with a mass of m and a charge of z.
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Example of PFTBA EI+
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Chemical IonizationSoft Ionization Techniques
RemovableIonizationVolume
Lenses
Filament
e-To MassAnalyzer
EI Ion Volume
CI Ion VolumeCH4
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Reagent gas reactions (methane)
m/z 16, 15, 14
m/z 17
m/z 29
m/z 28
m/z 27
m/z 41
Positive Ion Chemical Ionization
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Proton transfer
Hydride abstraction
Adduct formation
4252
45
HCHMHCM
CHHMCHM
6252 HCHMHCM
5353
5252
HCMHCM
HCMHCM
[M+1]+
[M-1]+
[M+29]+
[M+41]+
Positive Ion Chemical Ionization
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Common PICI Reagent Gases
• Methane [CH5+ & C2H5
+]– Protonates most organic molecules
– C2H5+ reacts with alkanes primarily by hydride abstraction
• Isobutane [C4H9+]
– Low purity (ion source gets dirty quickly)
• Anhydrous ammonia [H+(NH3)n=1-3]– Very selective protonation (nitrogen compounds)
– Forms [M+NH4]+ adduct with many compounds
– Keeps ion source clean
– Highly corrosive (short mech. pump lifetime)
• 549 & 687
• 821
• 858
Reagent GasProton
Affinity*
• 1126 & 1135
• 976
• 825
Hydride IonAffinity*
Lessfragmentation
withhigher PA
Less[M-H]+
withlower HIA
* kJ/mol
reaction must be exothermic, i.e., PA (analyte) > PA (reagent gas)
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EI Spectrum of Heptachlor
Intensity is low for any single m/z ion.
PICI Spectrum of Heptachlor
Intensity is concentrated in [M+H]+ ion.
Spectrum is simpler.
EI vs.PICI for Pesticides
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Adduct Formation in PICI
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Negative Ion Chemical Ionization (EC-NICI)
• Reagent gas reactions (methane)
• Kinetic energy of electrons reduced by collisions with reagent gas
• Resonance electron capture mechanism of ionization
*44 )70( eCHeeVCH
Thermal electron
HeatABeAB * [M]-
• Reagent gas reacts with electrons to form “plasma” of thermal electrons
• Ionization is favored by molecules which have a high electron affinity – electron capture
• Useful for selective analysis in heavy matrices, e.g., pesticides in food or waste matrix.
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Common NICI Reagent Gases
• Methane
• Isobutane– Low purity (ion source get dirty quickly)
• Carbon dioxide– Can produce less fragmentation than methane or
isobutane
• Anhydrous ammonia– Keeps ions source clean
– Highly corrosive (short mech. pump lifetime)
Reagent Gas
• 8.6x10-10
• ~2.1x10-9
• 5.8x10-9
• 5.9x10-9
e- ThermalizationRate*
Bettersensitivitywith higher
rate* cm3/s
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Negative Ion spectrum of the PFPA/PFPOH derivative of 11-nor-9-Carboxy-D9-THC
NICI of Carboxy THC - PFPA
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753
Pentafluoropropionyl (PFP) Derivatives of Norepinephrine, Epinephrine and Dopamine
Analysis of Catecholamines using NICI-MS
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Ion Trap vs QuadrupoleBasic Principles
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Voltage Relationship During a Mass Scan (Quadrupole)
VRF
V+180°
RF
+Vdc
-Vdc
+1500
-1500
Complete Mass Scan
RF
Po
ten
tial
DC
Po
ten
tial
+250
0
-250
m/z
77001-1380970608
+/-(U+Vocost)
-/+(U+Vocost)Ion beam
• Ions scanned by varying the DC/Rf voltage across the quadrupoles
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What is a Quadrupole Ion Trap?
tcosV
zo
ro
EntranceEndcap
ExitEndcap
RingElectrode
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0 90 180 270 360R F P h ase (d e g )
-150
-100
-50
0
50
100
150
Rin
g V
olta
ge (
V)
r r
r
z z z
VVV
Potential Energy Surfaces (Ion Traps)
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aZ
0.4
0.2
0
-0.2
-0.4
-0.6
0.5 1.0 1.5
Operating line for Mass selective stability
r stability
1.0
0.9
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4 0.30.3
0.20.1
1.0
0.2
Z
X, Y
Operating line formass selective instability
z stability
q ~.91cut-off
qz
qz = m(r + 2
O O2 2 2
Z )
m(r + 2z ) O O
2 2 2
8eV
az = 16eU
q Z
General Principles of Stability Diagrams
• Basic Ion Trap Principles– Mathieu stability diagram and stability/reduced
parameters
• Ion trap function : “Mass Selective Instability”
• Quadrupole: Mass Selective Stability mode of scanning
• The (a,q) coordinates are simply related to m/z and the operating voltage - whereas values are related to ion motion
tcosVU
zo
ro 0a
0U
z
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Stability Line and Mass Selective Ejection
0az/m
Vq
z
z
1.0
0.0 qz
az
0.908
Mass-selective Instability ScanningRamp RF voltage (V) to sequentiallyeject ions from low m/z to high m/z.
476 kHz
*
Mass-selectiveInstability Scanwith ResonantEjection
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+
Trapping Injected Ions
++++ ++
22o
2
zmz4
eVD
tcosV
zo
ro
• Correct RF voltage
• Helium buffer gas
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V
Eject (V’)
Gate Lens
Multiplier
Full Scan MS Scan Function
AGC Prescan*
Mass Analysis Scan
Ion Injection
Mass Analysis
Ion Injection
Mass Analysis
One complete scan constitutes a “microscan”
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1
10
100
1000
10000
100000
1 10 100 1000 10000 100000 1000000 10000000
Amount of Sample (arbitrary units)
Num
ber
of Io
ns
Tra
pped
(ar
bitr
ary
units
)Fixed Ion Injection Time
10 m
s
0.1 m
s
SpaceChargeEffects
DYNAMIC RANGE: ~103
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Ion Injection Time Optimized with AGC
250
ms*
5 µs*
*
SpaceChargeEffects
DYNAMIC RANGE: >106
Variable Time
* UserSelectable
** 5 µs PolarisQ,
10 µs LCQ,30 µs GCQ
1
10
100
1000
10000
100000
1 10 100 1000 10000 100000 1000000 10000000
Amount of Sample (arbitrary units)
Num
ber
of Io
ns
Tra
pped
(ar
bitr
ary
units
)
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Polaris Q Tune Parameters (AGC and Injection RF)
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Quadrupole vs. Ion Trap
Transmits one m/z ion at a time
Mass-Selective Stability scanning
Trap all m/z ions simultaneouslyMass-Selective Instability scanning
Quadrupole
Ion Trap
In full scanion traps are
more sensitive than quadrupoles.
quadrupoles use SIM to enhance
sensitivity
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Quadupoles and Sensitivity
• Duty cycle is important for determining mass analyzer efficiency
• Efficiency of the mass analyzer:
• Ionization and mass analysis occur simultaneously: Mass resolution and scan range are important when determining duty cycle
Transmits one m/z ion at a time
Mass-Selective Stability scanning
Quadrupole
Duty Cycle for a Quadrupole
Width of transmitted ion
total width of m/z range= Duty Cycle
DutyCycleEE onTransmissierMassAnalyz
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SIM, MIM and SRM,MRM (Target Compound Techniques)
• Single Quadrupole Technology (single-stage MS techniques)– SIM (Selected or Single Ion Monitoring)
• Set quadrupole to pass a single characteristic ion during a retention time window in the chromatogram
• Increases sensitivity 10-100X
• Lose spectral specificity
– MIM (Multiple Ion Monitoring)• Monitor 2 to 5 characteristic ions in addition to SIM quanitiation ion
• Set acceptable qualifier ion “ratios” to confirm detection
• More qualifier ions boost confidence but reduce sensitivity gains
• Triple Quadrupole Technology (MS/MS Techniques)
– SRM (Single Reaction Monitoring)• Single product ion monitored
– MRM (Multiple Reaction Monitoring)• Multiple product ions monitored
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Ion Traps and Sensitivity
• Efficiency of the mass analyzer:
• Ionization and mass analysis occur consecutively: Scan time (or rate) relative to ion accumulation is important for determining duty cycle
Duty Cycle for an Ion Trap
Ion Accumulation Time (ion gate time)
Total scan time= Duty Cycle
Trap all m/z ions simultaneouslyMass-Selective Instability scanning
External Source Ion Trap
DutyCycleEE onTransmissierMassAnalyz
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Tandem MS Principles
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Tandem Mass SpectrometryWhy use MS/MS?
• Enhanced Selectivity (Qualitative and Quantitative)– TRACE Analyses Criteria for Target Compounds
• Sensitivity and Selectivity are important– MS/MS Improves Trace Level Analyses in complex matrices and enhances
confirmatory analyses (Enhanced confirmation of identification)
• Combined with Soft Ionization techniques– Most signal in [M+H]+ ions; Added selectivity and s/n– Confirmatory assays (MW ions plus 2-3 unique ions)– Qualitative and quantitative with digital reagent gas flow
• Structural Characterization Applications– MS/MS provides unique evidence to an unknowns identity providing further
information about fragments in the MS spectrum
S/N
TRACE DSQ uses SIM to increase S
Polaris Q uses MS/MS to reduce N
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MS/MS “Tandem-In-Space”Triple Stage Quadrupole Technology
MS/MS “Tandem-In-Time”Ion Trap Technology MS/MS and MSn Capability
MS/MS “Tandem-In-Time”Ion Trap Technology
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MS/MS in an Ion Trap
1. Inject
2. Isolate
3. Fragment
4. Detect
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0az/m
Vq
z
z
1.0
0.0 qz
az
0.908
476 kHz
*
Mass-selectiveInstability Scanwith ResonantEjection
How MS/MS works
qz Mp = VRF
υ(ion) = (n + β) Ω/2
How Do We Isolate Ions for MS/MS?
Ion we wish to isolate
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m/z 1000
m/z 300
m/z 100
Fast FourierTransform
Isolation Waveforms
Time Domain Frequency Domain
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CID using Resonant Excitation
0.908
qz
0.0
t=15 ms
0.908
qz
0.0
Product ions
How MS/MS works
qz Mp = VRF
υ(ion) = (n + β) Ω/2
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Polaris Q Excitation Event Characteristics
P = precursor mass
Excitation “q”
0.225
0.300
0.450
qz
The choice of ‘q’ is also a function of the MS/MS lower limit of the product ion m/z range. A ‘q’ of 0.225 is 1/4Mp (where Mp is the m/z of the parent ion), and a ‘q’ of 0.3 is 1/3Mp, and a ‘q’ of 0.45 is 1/2Mp. For example, if a ‘q’ of 0.45 is used, and Mp is m/z 400, then the daughter ion lower limit that can be observed in the spectrum will be m/z 200. If the same ‘q’ is used for an Mp at m/z 800, then the daughter ion lower limit that can be observed will be m/z 400, and so on
Stability Diagram: Where parent ions reside on the q axis during the excitation event
z/m
Vqz
MS/MS
qz Mp = VRF
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Higher qz Means Higher Energy
e16
zmq
mz4
eVD
2
o
22
z
22
o
2
z
qz = 0.225 0.30 0.45
Dz
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Resonant Excitation qz Value
0.908
qz
0.00.225
0.908
qz
0.0
0.908
qz
0.0
0.30
0.45
Fragment ionsnot trapped
Product Ionm/z Range
FragmentationEnergy
1/4
1/3
1/2
x
2x
4x
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V
Eject (V’)
Gate Lens
Multiplier
Tandem MS: Polaris Q MS/MS Scan Function
AGC Prescan
Mass Analysis Scan
Ion Injection
Mass Analysis
Ion Injection
Mass Analysis
Isolate
Ion Isolation
Ion IsolationResonant
Excitation
Excite
How MS/MS works for all RF-Traps
qz Mp = VRF
υ(ion) = (n + β) Ω/2
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MS/MS Example - Chlordane
GC/MS Spectrum GC/MS/MS Product Ion Spectrum
Isolation ofPrecursor Ion
FragmentPrecursor Ion
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Polaris Q MS/MS Parameters
MS/MS Parameters
Choice of Excitation q’s
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MS/MS: Optimizing Conditions
Dexamethasone Product ion intensity vs Collision Voltage
0.E+00
1.E+05
2.E+05
3.E+05
4.E+05
5.E+05
6.E+05
7.E+05
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Collision Voltage (p-p)
Pro
du
ct Io
n In
ten
sity
‘q’ is a function of the RF voltage applied to the ring electrode during excitation
Excitation Event – higher excitation ‘q’s may provide improved conversion efficiencies (ECID = Fi / P0)