Introduction of Mass spectrometry, principle, and its application

Table of Contents

Introduction of mass spectrometry: Mass spectrometry is an analytical spectroscopic technique that involves the ionization of molecules of compounds by bombarding with an energetic electron beam followed by separating and analyzing the fragments in terms of mass/charge ratio. Mass spectrometry identifies molecules based on their m/e ratio. It has wide application in qualitative and quantitative analysis.

Mass spectrometry principle

In mass spectrometry, a given compound is vaporized first and then the molecules of the compound are bombarded with an energetic electron beam. Due to collision, the energy of electrons is transferred to molecules which in turn emit electrons to produce positively charged ions called molecular ions or parent ion or biradical cation. These molecular ions are highly energized and often undergo fragmentation to give many smaller positive ions called daughter ions. Each of the daughter ions has a certain value of m/e charge. Mostly the ions produced in fragmentation carry a +1 charge hence, m/e usually represents the mass of the ion.

Thus, obtained molecular and daughter ions are passed through an electric field and strong magnetic field. Therefore, molecular and daughter ions having a m/e ratio get separated and collected at the detector.

A signal is obtained corresponding to each m/e value and the intensity of the signal is proportional to the number of ions giving rise to the signal.

Mass spectrometry fragmentation

Mass spectrometry fragmentation of Benzamide is shown:

introduction to mass spectrometry
Fragmentation of Benzamide in mass spectrometry

Mass spectrometry graph

A mass spectrum is a graph between relative abundance or intensity versus the m/e value of ions. The mass spectrometry graph of Benzamide is shown below:

Mass spectrometry graph
Mass spectrum of benzamide

Base peak in mass spectrometry

The ions formed by removing one electron from the parent molecules are known as molecular ions or parent ions and the corresponding largest peak found in the mass spectrum is called base peak or parent peak. The molecular ion peak is usually denoted by M+. It may or may not be the peak of the highest intensity. The molecular ion is the most important ion as its mass is the molecular mass of the parent molecule.

Mass spectrometry of hexane

Mass spectrometry of hexane
fragmentation of hexane in mass spectrometry

Mass spectrometry instrumentation

The block diagram of the typical mass spectrometer is shown below:

Mass spectrometry instrumentation
Block diagram of a mass spectrometer

Different types of ionization techniques in mass spectrometry

The most common types of ionization techniques in mass spectrometry are listed below:

  1. Electron impact ionization
  2. Chemical ionization
  3. Field desorption ionization
  4. Fast atom boambardment ionization
  5. Plasma desorption ionization
  6. Laser desorption ionization
  7. Thermospray mass spectrometry
  8. Electrospray mass spectrometry

Types of analyzers in mass spectrometry

The mass analyzer is the heart of each mass spectrometer which separates the mixture of ions that are generated during the ionization step by m∕z in order to obtain a spectrum. There are several different types of analyzers with different characteristics

  1. Magnetic sector mass spectrometer
  2. Quadrupole mass spectrometer
  3. Ion trap mass spectrometer
  4. Time of flight mass spectrometer
  5. Fourier transform mass spectrometer

Uses of mass spectrometry

Mass spectrometry has both qualitative and quantitative uses.

A. Qualitative analysis

  1. Identification of unknown compound by comparing its spectra with known sample
  2. Determination of molecular structure by analyzing fragmentation patterns, and their relative intensities in mass spectrum.
  3. Characterization and determination of sequencing of amino acids in proteins.
  4. Determination of isotopic composition of elements within a sample.

B. Quantitative analysis

  1. Determination of molecular mass and molecular formula by observing mass spectrum and fragmentation pattern.
  2. It is widely used to determine the size of the nanoparticles.
  3. It is also applicable in biotechnology, pharmaceutical, clinical and environment.

Mass spectrometry video

Mass spectrometry video

FAQs/MCQs:

What is mass spectrometry?

Mass spectrometry is an analytical spectroscopic technique that involves the ionization of molecules of compounds by bombarding with an energetic electron beam followed by separating and analyzing the fragments in terms of mass/charge ratio.

What is the base peak in mass spectrometry?

The ions formed by removing one electron from the parent molecules are known as molecular ions or parent ions and the corresponding largest peak found in the mass spectrum is called base peak or parent peak.

What does mass spectrometry tell?

Mass spectrometry tells about the molecular mass and molecular structure of a compound.

What is the molecular ion in mass spectrometry?

The ions formed by removing one electron from the parent molecules are known as molecular ions.

Mass spectrometry

Share this to:

Leave a Reply

Your email address will not be published. Required fields are marked *