95 Questions
Which ionization technique uses electron bombardment, causing fragmentation?
EI
What is the best ionization technique for large biomolecules?
MALDI
Which ionization technique involves proton/electron transfer from a solid mixed with matrix?
MALDI
Which mass spectrometry technique has the highest resolution up to 10 million?
FT-ICR
Which ionization technique uses photoionization of reagent gas to induce analyte ionization?
APPI
Which mass spectrometry technique separates ions by flight time?
TOF
What type of analytes are best suited for analysis by APPI compared to electrospray ionization?
Non-polar compounds
How does APPI ionize analyte molecules that have ionization energies higher than the lamp output?
By using a reagent gas to transfer energy and produce ions
What is the role of reagent gas in APPI?
To produce ions from the analyte molecules through reactions
How does ESI produce multiple charged ions from analyte molecules?
By forming highly charged droplets that undergo fission
Why is multiple charging significant in mass spectrometry?
It helps in detecting high mass analytes outside the detection range
What happens as highly charged droplets shrink in size during ESI?
The charge becomes concentrated on the analyte molecules
What is the main purpose of the third quadrupole in mass spectrometry?
To provide a sensitive and selective detection mode for targeted analytes
In electrospray ionization, which type of molecules ionize best?
Polar, charged molecules
What is one key advantage of matrix-assisted laser desorption ionization (MALDI) compared to other techniques?
Simple spectra
What factor plays a significant role in influencing the resolution of a mass spectrometer?
Ion kinetic energy spread
How does Fourier transform ion cyclotron resonance (FT-ICR) achieve high resolution in mass spectrometry?
By trapping ions in a magnetic field and exciting their cyclotron motion
What principle does ion mobility spectrometry rely on to separate ions?
Drift time in buffer gas
What is the main function of a time-of-flight (TOF) mass analyzer?
Separating ions based on their m/z ratios
How does an orbitrap mass analyzer achieve high mass resolution?
By trapping ions between an inner spindle and outer barrel electrostatically
"Which of the following factors does NOT influence the ionization efficiency of an analyte in electrospray ionization?"
Analyte volatility
What is the main limitation of matrix-assisted laser desorption ionization (MALDI)?
Limited mass accuracy
How does a quadrupole mass analyzer selectively transmit ions based on their m/z?
By applying both RF and DC voltages to four parallel rods and scanning RF/DC voltages to allow ions with specific m/z to traverse based on stable trajectory
What is a key advantage of ion trap mass analyzers over quadrupole mass analyzers?
Higher trapping efficiencies and multi-stage MS/MS capabilities
How does time-of-flight mass spectrometry achieve high resolving power and mass accuracy?
By separating ions based on their time-of-flight down a field-free drift tube
What structural information does ion mobility spectrometry (IMS) provide compared to conventional mass spectrometry?
Charge and rotationally averaged collision cross section information
What does infrared multiphoton dissociation (IRMPD) induce in ions?
Energy deposition through absorption of IR photons for peptide backbone cleavages
How does Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) detect ions?
By trapping ions in a magnetic field and exciting their cyclotron motion with an electric field
What does ultraviolet photodissociation (UVPD) induce in ions compared to CID?
More amide backbone cleavages through absorption of multiple UV photons
What role does multiple reaction monitoring (MRM) mode play in triple quadrupole mass spectrometers?
Isolating precursor ions in the first quadrupole and fragmenting them in the second quadrupole via CID
How is mass defect used to determine molecular formulas from high-resolution mass spectra?
By using isotopic patterns and mass defects to calculate possible molecular formulas within a certain error threshold
Which mass spectrometry technique offers high resolution and accuracy at a lower cost than FT-ICR?
EI
Which ionization method is best suited for analyzing volatile thermally-stable compounds?
ESI
Which mass spectrometry technique forms charged droplets that undergo coulombic fission?
APPI
Which mass spectrometry technique is known for having the highest resolution up to 10 million?
FT-ICR
Which ionization technique involves proton/electron transfer from a solid mixed with matrix?
MALDI
Which mass spectrometry technique separates ions by flight time and provides very high resolution up to 100,000?
TOF
What is the role of the reagent gas in atmospheric pressure photoionization (APPI)?
Transferring energy to ionize the analytes
Why does electrospray ionization (ESI) work better than APPI for polar compounds?
The charge becomes concentrated on the analyte molecules in ESI
How does APPI ionize molecules with ionization energies higher than the lamp output?
By transferring energy to the analyte molecules through reactions
In electrospray ionization (ESI), why are highly charged ions more readily dissociated during tandem MS experiments?
Highly charged ions have stronger coulombic interactions
What is a key difference between atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) in terms of ionizing analytes?
APPI forms singly charged ions, while ESI forms multiple charged ions
What makes multiple charging significant in mass spectrometry when analyzing high mass analytes?
**Highly charged ions are more readily dissociated during tandem MS experiments
What advantage do ion trap mass analyzers offer over quadrupole mass analyzers?
Multi-stage MS/MS capabilities
How do ions get separated in ion mobility spectrometry (IMS)?
By their drift times in an electric field
What is the main limitation of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS)?
Limited mass range
In UVPD, how does the fragmentation compare to CID?
More amide backbone cleavages
What does Reflectron TOF use to improve resolution in time-of-flight mass spectrometry?
Ion mirror
How is mass defect utilized in determining molecular formulas from high-resolution mass spectra?
It reflects isotopic patterns
What type of dissociation occurs in infrared multiphoton dissociation (IRMPD) compared to CID?
Cleavages along peptide backbone
What does a quadrupole mass analyzer offer over an ion trap analyzer?
Wider mass range
What principle does time-of-flight mass spectrometry rely on for ion separation?
Drift times in an electric field
How does multiple reaction monitoring (MRM) mode differ from standard analysis in triple quadrupole mass spectrometers?
Precursor ion isolation only
What is the primary function of the third quadrupole in mass spectrometry?
Transmit only one fragment ion to the detector
In electrospray ionization, which type of analyte molecules ionize the best?
Polar, charged molecules
How does matrix-assisted laser desorption ionization (MALDI) produce gas phase ions from solid samples?
Laser ablation of solid sample mixed with matrix
What is the key principle in ion separation in a quadrupole mass filter?
RF and AC voltages
Why is time-of-flight (TOF) mass analyzer known for its high resolution capabilities?
Pulsed ion injection for m/z dependent flight times
What does Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry trap ions in?
A magnetic field
What role does ion mobility spectrometry play when coupled with mass spectrometry?
Providing structural information based on drift time in buffer gas
How do orbitrap mass analyzers achieve high mass resolution?
By trapping ions electrostatically and inducing radial oscillations
What additional information does ion mobility spectrometry provide when coupled with mass spectrometry?
Structural details based on drift time in buffer gas
What does MALDI primarily use to ablate solid samples mixed with UV-absorbing matrix?
Laser energy
What role does the reagent gas play in atmospheric pressure photoionization (APPI)?
It helps in transferring energy to produce ions from analyte molecules
Why does electrospray ionization (ESI) work better than APPI for polar compounds?
Polar compounds are less likely to form multiple charged ions in ESI
What is the primary reason that highly charged ions are more readily dissociated during tandem MS experiments?
Highly charged ions have concentrated charge on analyte molecules
In electrospray ionization (ESI), what happens as highly charged droplets shrink in size?
The charge becomes concentrated on the analyte molecules
What is the significance of multiple charging in mass spectrometry when analyzing high mass analytes?
It allows detection of high mass analytes within the instrument's detection range
What type of compounds are best suited for analysis by atmospheric pressure photoionization (APPI) compared to electrospray ionization?
Non-polar compounds difficult to ionize by ESI
Which mass spectrometry technique offers the highest resolution up to 10 million?
Fourier Transform Ion Cyclotron Resonance (FT-ICR)
What is the main function of a quadrupole mass analyzer?
Selective ion transmission based on m/z
Which ionization technique is best suited for analyzing large biomolecules?
Matrix-Assisted Laser Desorption Ionization (MALDI)
In mass spectrometry, which technique forms charged droplets that undergo coulombic fission?
Electrospray Ionization (ESI)
What is a key advantage of Time-of-Flight (TOF) mass spectrometry compared to Quadrupole mass analyzers?
Separates ions by flight time
Which ionization technique uses photoionization of reagent gas to induce analyte ionization?
Atmospheric Pressure Photoionization (APPI)
How does a quadrupole mass analyzer selectively transmit ions based on their m/z?
By scanning RF/DC voltages and amplitudes
What is the main advantage of ion trap mass analyzers over quadrupole mass analyzers?
High trapping efficiencies
How does time-of-flight mass spectrometry achieve high resolving power and mass accuracy?
By separating ions based on their flight time down a drift tube
What additional information does ion mobility spectrometry provide compared to conventional mass spectrometry?
Collision cross section of ions
How does infrared multiphoton dissociation (IRMPD) differ from collision-induced dissociation (CID) in terms of fragmentation?
IRMPD causes extensive cleavages along the peptide backbone
How is mass defect utilized in determining molecular formulas from high-resolution mass spectra?
It calculates possible molecular formulas based on isotopic patterns
What is one key strength of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS)?
Extremely high resolution and accurate mass measurements
What does ultraviolet photodissociation (UVPD) primarily induce in ions compared to CID?
More amide backbone cleavages
What is the principle of operation for ion mobility spectrometry (IMS)?
Separates ions based on drift times in an electric field
How does infrared multiphoton dissociation (IRMPD) differ from collision-induced dissociation (CID) in terms of fragmentation?
IRMPD induces cleavages along the weakest bonds
What is the main advantage of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers over other types?
High resolution and accurate mass measurement
In ion mobility spectrometry (IMS), what property of ions determines their drift time in the buffer gas?
Collision cross section
What is a key limitation of time-of-flight (TOF) mass analyzers compared to other mass analyzer types?
Limited mass range
Which factor plays a crucial role in achieving high resolution in a mass spectrometer using orbitrap technology?
Flight path length
What is a characteristic feature of matrix-assisted laser desorption ionization (MALDI) spectra?
Simple spectra with high reproducibility
How does a quadrupole mass filter function as a mass analyzer?
By selectively transmitting ions based on stable trajectory
One of the key advantages of ion mobility spectrometry (IMS) coupled with mass spectrometry (MS) is its ability to:
Provide additional structural information
Which factor does NOT significantly influence the resolution of a mass spectrometer?
$pK_a$ values of analytes
'High resolution, accuracy, and duty cycle' are the key strengths of which type of mass analyzer?
Time-of-flight mass analyzer
What is the primary function of the third quadrupole in a mass spectrometer?
Transmission of fragment ions to the detector
Study Notes
Quadrupole Mass Analyzer
- Consists of four parallel rods with RF and DC voltages applied
- Ions with specific m/z traverse the quadrupole based on their stable trajectory, filtering out others
- Scanned voltages build up a mass spectrum one m/z at a time
Ion Trap Mass Analyzer
- Offers high trapping efficiencies, multi-stage MS/MS capabilities, and ion storage/accumulation
- Limited mass range and susceptible to space charge effects
- Contrasted with quadrupole analyzers: wider mass range, faster scan speeds, and less susceptible to space charge
Time-of-Flight Mass Spectrometry (TOF-MS)
- Separates ions based on time-of-flight down a field-free drift tube
- Ions of the same m/z reach the detector at the same time, regardless of kinetic energy
- Long flight path improves separation; Reflectron TOF increases effective flight path length
Ultraviolet Photodissociation (UVPD)
- Deposits energy into ions through absorption of multiple UV photons
- Induces dissociation through direct bond cleavages, resulting in more amide backbone cleavages compared to CID
Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
- Traps ions in a magnetic field, exciting their cyclotron motion with an electric field
- Induces a detectable image current, yielding extremely high resolution mass spectra
- Offers the highest resolution and most accurate mass measurements
Ion Mobility Spectrometry (IMS)
- Separates ions in a buffer gas based on drift times, depending on charge and rotationally averaged collision cross section
- Provides additional structural information to mass alone
- IMS-MS aids compound identification for applications like proteomics and metabolomics
Infrared Multiphoton Dissociation (IRMPD)
- Deposits energy into ions through absorption of multiple IR photons, inducing cleavages along the weakest bonds
- Results in more extensive fragmentation than low-energy CID, often cleaving along the peptide backbone
Mass Defect
- Difference between the exact mass of an atom or molecule and its whole mass unit assignment
- Used to calculate possible molecular formulas from ultrahigh resolution spectra within a certain error threshold
Multiple Reaction Monitoring (MRM)
- Isolates precursor ions in the first quadrupole, fragments them via CID in the second quadrupole
- Transmits only one fragment ion to the detector in the third quadrupole
- Provides a sensitive, selective detection mode for targeted analytes and metabolites in complex samples for quantitative purposes
Electron Ionization (EI)
- Uses a 70eV electron beam to ionize samples, causing extensive fragmentation
- Incident electrons eject outer shell electrons, leaving the sample with a net positive charge
- Excited species undergo unimolecular decomposition, ejecting molecular fragments
Electrospray Ionization (ESI)
- Produces multiple charged ions from analyte molecules in solution
- Multiple charging occurs due to concentration of charge on analyte molecules during solvent evaporation and coulombic fission
- Allows detection of high mass analytes with m/z values outside the instrument's detection range
Atmospheric Pressure Photoionization (APPI)
- Uses a krypton or xenon discharge lamp to ionize a reagent gas, transferring energy to produce ions from the analyte molecules
- Suited for non-polar compounds that are difficult to ionize by ESI
Matrix-Assisted Laser Desorption Ionization (MALDI)
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Uses a laser to ablate a solid sample mixed with a UV-absorbing matrix
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Matrix absorbs laser energy and transfers protons to analyte molecules, forming mainly [M+H]+ ions
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Key advantages: ability to analyze non-volatile biomolecules and simple spectra; limitations: limited mass accuracy and reproducibility between shots### Ionization Techniques
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EI (Electron Ionization) uses a 70eV electron beam to ionize samples, causing extensive fragmentation and producing characteristic fragmentation patterns.
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EI is best for volatile thermally-stable compounds.
-
MALDI (Matrix-Assisted Laser Desorption Ionization) uses a laser to ablate a solid sample mixed with an UV-absorbing matrix, producing mainly [M+H]+ ions.
-
MALDI is suited for large biomolecules.
-
ESI (Electrospray Ionization) forms charged droplets that undergo coulombic fission, producing multiple charged ions.
-
ESI is suited for polar compounds in liquid samples.
-
APPI (Atmospheric Pressure Photoionization) uses photoionization of reagent gas to induce analyte ionization.
-
APPI is suited for non-polar compounds that are difficult to ionize by ESI.
Mass Analyzers
- TOF (Time-of-Flight) separates ions by their time of flight down a field-free drift tube, offering high resolution up to 100,000, fast analysis, and a wide m/z range.
- Quadrupole separates ions by selectively transmitting ions of a given m/z using RF and DC voltages, offering a simple design, robustness, and high sensitivity and speed for scanning.
- FT-ICR (Fourier Transform Ion Cyclotron Resonance) detects image current from ion cyclotron resonance, offering the highest resolution up to 10 million and excellent mass accuracy.
Mass Spectrometry Techniques
- IRMPD (Infrared Multiphoton Dissociation) deposits energy into ions through absorption of multiple photons, inducing cleavages along the weakest bonds.
- UVPD (Ultraviolet Photodissociation) deposits energy into ions through absorption of multiple UV photons, inducing dissociation through direct bond cleavages.
- CID (Collision-Induced Dissociation) involves vibrational activation and lower energy cleavages, often retaining side chains.
- MRM (Multiple Reaction Monitoring) mode is used in triple quadrupole mass spectrometers for targeted, quantitative analysis.
Ion Mobility Spectrometry
- IMS separates ions by drift time in a buffer gas, which depends on rotationally averaged collision cross section.
- IMS provides additional structural information to mass spectrometry, aiding compound identification in applications like proteomics and metabolomics.
Mass Defect and Molecular Formulas
- Mass defect is the difference between the exact mass of an atom or molecule and its whole mass unit assignment.
- Isotopic patterns and mass defects can be used to calculate possible molecular formulas from ultrahigh resolution spectra within a certain error threshold.
Test your knowledge on the ionization and fragmentation processes that occur during Electron Ionization (EI) in mass spectrometry. Learn about the use of a 70eV electron beam to ionize samples and the extensive fragmentation it can cause.
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