24 Questions
Which ionization type is most commonly used with a liquid feed?
Inductively Coupled Plasma (ICP)
What is the primary characteristic of Electrospray Ionization (ESI)?
It gives very little fragmentation.
Which ionization type is commonly used for solid samples?
Matrix Assisted Laser Desorption Ionization (MALDI)
What is the characteristic of Atmospheric Pressure Chemical Ionization (APCI)?
It gives some fragmentation.
Which of the following ionization types is not commonly used with a gas phase?
Electrospray Ionization (ESI)
What is the characteristic of Desorption Electrospray Ionization (DESI)?
It is a type of portable ionization.
Which ionization type is commonly used for elemental analysis?
Inductively Coupled Plasma (ICP)
What is the primary characteristic of Matrix Assisted Laser Desorption Ionization (MALDI)?
It is commonly used for solid samples.
What is the purpose of the vacuum pick up line in DESI?
To collect the resulting ions
What is the main difference between ESI and DESI?
The way the sample is ionized
What is the function of the corona needle in APCI?
To charge the droplets
What type of molecules are typically analyzed using ESI?
Large biomolecules
What is the purpose of the matrix in MALDI?
To absorb the laser light
What is the result of no fragmentation in ESI?
Multiple peaks are observed, including M+H+, M+Na+, and isotopic peaks
What is the typical use of DESI?
For remote MS analysis of untreated surfaces
How many different proteins does the human body have?
100,000
What is the primary ionization technique used in Electron Ionization (EI)?
Bombardment of the analyte with electrons
What is the result of the fragmentation process in Electron Ionization (EI)?
The formation of multiple, charged fragments
What is the characteristic of Chemical Ionization (CI) compared to Electron Ionization (EI)?
It produces less fragmentation
What is the type of ion typically formed in Chemical Ionization (CI)?
A protonated ion (M+H+)
What is the process by which ions are formed in Electrospray Ionization (ESI)?
Nebulization of the analyte with a high voltage
What is the characteristic of Electrospray Ionization (ESI) compared to other ionization techniques?
It produces less fragmentation
What type of ions are commonly formed in Electrospray Ionization (ESI)?
Both singly-charged and multiply-charged ions
What is the common peak observed in Electrospray Ionization (ESI) in positive ion mode?
M+H peak
Study Notes
Mass Spectrometry (MS)
- Mass Spectrometry is a technique used to analyze the composition of a sample by breaking it down into charged particles (ions) and measuring their mass-to-charge ratio.
Gas Phase Ionization
- Electron Ionization (EI): a heated tungsten filament produces electrons that “bombard” the analyte molecules, causing ionization through loss of an electron (for positive polarity MS).
- EI results in more lower m/z fragments due to further decomposition/fragmentation of the ionized molecules.
- Chemical Ionization (CI): a “softer” ionization technique that results in less fragmentation, possible in both negative and positive ion modes.
Liquid Samples
- Electrospray Ionization (ESI): a soft ionization technique that produces molecular (or M+H+/M-H-) ions, often resulting in multiply-charged species (e.g., proteins and biomolecules).
- ESI is efficient for charging polar/ionic compounds, including very large compounds, with almost no fragmentation.
Ionization Types
- Inductively Coupled Plasma (ICP): liquid feed, gives elements, lots of fragmentation.
- Electron Impact (EI): gas phase, lots of fragmentation.
- Chemical Ionization (CI): gas phase, some fragmentation.
- Electrospray (ESI): liquid, very little fragmentation.
- Atmospheric Pressure Chemical Ionization (APCI): liquid, some fragmentation.
- Matrix Assisted Laser Desorption Ionization (MALDI): solid, some fragmentation.
- Desorption Electrospray Ionization (DESI): portable, very little fragmentation.
Separation Types (Ion Filters/Mass Analyzers)
- Magnetic Sector: slow, acceleration in magnetic field, moderate cost.
- Double Focusing: slow, magnetic plus electric field, high cost.
- Quadrupole: fast, passage through ac electric field, moderate cost.
- Ion trap: fast, orbit in quadrupole, moderate cost.
- Time-of-Flight: very fast, time to travel through tube, moderate cost.
- Newer High Resolution: varies, various, usually involving orbits, high cost.
Detectors
- Electron Multiplier: yes, fairly common.
- Microchannel plate: yes, higher-end instruments.
- Faraday Cup: no.
Other Ionization Techniques
- DESI – Desorption Electrospray Ionization: uses electrospray focused onto the sample to produce ionization, commonly used for remote MS analysis of untreated surfaces.
Applications
- Proteins and Peptides: human has 100,000 different proteins, often analyzed using MS techniques like ESI and MALDI.
This quiz covers the different ionization techniques used in mass spectrometry, including electron ionization and its principles.
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