Mass Spectrometry Ionization Techniques

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Questions and Answers

Which ionization type is most commonly used with a liquid feed?

Atmospheric Pressure Chemical Ionization (APCI)

Chemical Ionization (CI)

Inductively Coupled Plasma (ICP) (correct)

Electron Impact (EI)

What is the primary characteristic of Electrospray Ionization (ESI)?

It gives some fragmentation.

It gives lots of fragmentation.

It gives very little fragmentation. (correct)

It does not give fragmentation.

Which ionization type is commonly used for solid samples?

Matrix Assisted Laser Desorption Ionization (MALDI) (correct)

Electron Impact (EI)

Chemical Ionization (CI)

Desorption Electrospray Ionization (DESI)

What is the characteristic of Atmospheric Pressure Chemical Ionization (APCI)?

It gives some fragmentation. Signup and view all the answers

Which of the following ionization types is not commonly used with a gas phase?

Electrospray Ionization (ESI) Signup and view all the answers

What is the characteristic of Desorption Electrospray Ionization (DESI)?

It is a type of portable ionization. Signup and view all the answers

Which ionization type is commonly used for elemental analysis?

Inductively Coupled Plasma (ICP) Signup and view all the answers

What is the primary characteristic of Matrix Assisted Laser Desorption Ionization (MALDI)?

It is commonly used for solid samples. Signup and view all the answers

What is the purpose of the vacuum pick up line in DESI?

To collect the resulting ions Signup and view all the answers

What is the main difference between ESI and DESI?

The way the sample is ionized Signup and view all the answers

What is the function of the corona needle in APCI?

To charge the droplets Signup and view all the answers

What type of molecules are typically analyzed using ESI?

Large biomolecules Signup and view all the answers

What is the purpose of the matrix in MALDI?

To absorb the laser light Signup and view all the answers

What is the result of no fragmentation in ESI?

Multiple peaks are observed, including M+H+, M+Na+, and isotopic peaks Signup and view all the answers

What is the typical use of DESI?

For remote MS analysis of untreated surfaces Signup and view all the answers

How many different proteins does the human body have?

100,000 Signup and view all the answers

What is the primary ionization technique used in Electron Ionization (EI)?

Bombardment of the analyte with electrons Signup and view all the answers

What is the result of the fragmentation process in Electron Ionization (EI)?

The formation of multiple, charged fragments Signup and view all the answers

What is the characteristic of Chemical Ionization (CI) compared to Electron Ionization (EI)?

It produces less fragmentation Signup and view all the answers

What is the type of ion typically formed in Chemical Ionization (CI)?

A protonated ion (M+H+) Signup and view all the answers

What is the process by which ions are formed in Electrospray Ionization (ESI)?

Nebulization of the analyte with a high voltage Signup and view all the answers

What is the characteristic of Electrospray Ionization (ESI) compared to other ionization techniques?

It produces less fragmentation Signup and view all the answers

What type of ions are commonly formed in Electrospray Ionization (ESI)?

Both singly-charged and multiply-charged ions Signup and view all the answers

What is the common peak observed in Electrospray Ionization (ESI) in positive ion mode?

M+H peak Signup and view all the answers

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.

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Description

This quiz covers the different ionization techniques used in mass spectrometry, including electron ionization and its principles.