History and Introduction of Mass Spectrometry (MS)

History and Introduction of Mass Spectrometry (MS)

 

History and Introduction of Mass Spectrometry (MS)

Table of Contents

• History
• Introduction
• Principle
• Instrumentation
• Mass spectrum
• Applications

History

The earliest gas discharge experiments served as the foundation for mass spectrometry. This were carried out in a glass tube that had been partially emptied and into which electrodes had been placed. A number of glowing light phenomena were seen when the gas pressure and voltage across the electrodes were appropriate.

Wilhelm Wien, a German scientist, discovered in 1898 that charged particle beams could be deflected by a magnetic field, which established the groundwork for mass spectroscopy. British physicist J.J. Thomson, who had previously discovered the electron and seen its deflection through an electric field, conducted more complex experiments between 1907 and 1913 in which he passed a beam of positively charged ions throughout a combined magnetic and electrostatic field.

The two fields in Thomson's tube were positioned so that the ions were diverted in two perpendicular directions through tiny angles. In the end, the ions caused a series of parabolic curves to appear on a photographic plate that was in their path. Each parabola represented ions with a given mass-to-charge ratio, with the position of each ion depending upon the velocity. The lengths of the parabolic curves served as a measurement for the range of ion energies present in the beam. And afterwards, Thomson swapped out the photographic plate for a metal sheet that had a parabolic slit cut into it in an effort to assess the relative abundances of the various ion species present.

He was able to measure a current related to each distinct ion species by changing the magnetic field while going through a mass spectrum. As a result, he can be given credit for creating the first mass spectrograph and mass spectrometer.

Introduction

Mass spectrometry is a potent analytical technique that may be used to analyze known materials, detect unknown elements in a sample, and provides insight on the structure and chemical characteristics of various molecules. The entire procedure entails converting the sample into gaseous ions, with or without fragmentation, and characterizing those ions according to their relative abundances and mass to charge ratios (m/z).

This method essentially investigates how molecules are affected by ionizing energy. The consumption of sample molecules during the creation of ionic and neutral species depends on chemical events occurring in the gas phase.

Principle

A sample, which could be solid, liquid, or gas, is ionized during a conventional Mass Spectrometry operation, for example by being bombarded with an electron beam. This could result in some of the molecules in the sample fragmenting into positively charged parts or just becoming positively charged as a whole. Afterwards, these ions (fragments) are separated based on their mass-to-charge ratio, by accelerating them and exposing them to an electric or magnetic field; ions with the same mass-to-charge ratio will deflect equally. A system that can detect charged particles, such as an electron multiplier, is used to find the ions. Findings are shown as spectra of the detected ion signal strength as a function of mass-to-charge ratio. By comparing known masses (such as the mass of a complete molecule) to the identified masses or using a distinctive fragmentation pattern, it is possible to identify the atoms or molecules in the sample. A mass spectrometer exploits this characteristic of matter to map ions of different masses on a mass spectrum, which is based on Newton's second law of motion and momentum.

Instrumentation of Mass Spectrometry

It consists of four basic parts that are as follows,

1. Ionization Chamber

Ionizer - The electrons use bombardment to ionize the sample. Between the cathode and the anode, these electrons move. High-energy electrons knock electrons out of the sample as it passes through the electron stream between the cathode and anode, forming ions.

2. Accelerating Plates

Ions put between a pair of charged parallel plates in an accelerator are drawn to one plate and repelled by the other plate. By altering the charge on the plates, the acceleration speed may be managed.

3. Deflector

Ions are deflected by a magnetic field depending on their mass and charge. The least deflected ions are those that are big or have two or more positive charges. The most ion deflection occurs when an ion is light or has a single positive charge.

4. Detector

The right-charged and right-mass ions travel to the detector. The ion that strikes the detector is used to examine the mass to charge ratio.

Instrumentation

Mass Spectrum

A graph of the ion signal as a function of the mass-to-charge ratio is known as a mass spectrum. The masses of particles and molecules in a sample, as well as the chemical identity or structure of molecules and other chemical compounds, are all determined using these spectra.

Molecular Ion Peak

The peak that formed due to the removal of electrons from actual molecule during the process ionization, its m/z value is same as the mass of actual molecule. It is represented as M⁺ Peak. The peak that corresponds to the heaviest ion is called the molecular ion peak.

A molecular ion is created when an electrically neutral molecule releases one of its electrons. A group of two or more atoms that are covalently linked together or a metal complex that functions as a single entity and has a net charge that is greater than zero are referred to as molecular ions. The mass of a molecular ion is regarded as being equal to the mass of the molecule because the electron mass is so little in comparison to that of a molecule.

Base Peak

The tallest peak in the spectrum that shows 100% abundance is known as base peak. The ion that is most prevalent and plentiful is represented by the base peak.

Example

The molecular mass of pentane is 72, so the peak at 72 is the molecular ion peak and tall peak that have 100 % abundance on y-axis is known as base peak as shown in figure.

Mass Spectrum of Pentane

Applications of Mass Spectrometry

• The pharmaceutical sector values the use of mass spectrometry (MS) for biochemical applications. These consist of techniques for measuring molecular functions such ligand binding as well as compositional assessments of biomolecules, particularly proteins.
• Cataloging protein expression, describing protein interactions, and locating protein modification sites are the three main uses of MS in proteomics.
• Uses of mass spectrometry in pharmaceutical analysis include metabolite screening, preclinical development, pharmacokinetic and pharmacodynamics assessments, drug discovery, and absorption, distribution, metabolism, and elimination (ADME) research.