Mass Spectrometry

Mass spectrometry is a powerful analytical technique used to quantify known materials, to identify unknown compounds within a sample, and to elucidate the structure and chemical properties of different molecules. The complete process involves the conversion of the sample into gaseous ions, with or without fragmentation, which are then characterized by their mass to charge ratios (m/z) and relative abundances. 

Basic Principle:

The mass spectroscopy is based on the positive ion generation. 

Mass Spectrometry Assignment

For its most popular model, the electron impact ionization with magnetic sector analyzer, the sample under investigation is converted into vapor phase and bombarded with electrons having energy sufficient to knock out one electron from it (>10 eV) to produce a positively charged ion called molecular ion or parent ion which is denoted by M+. Positively charged molecule M+ is often unstable, and with increase in energy (10–70 eV) according to bond strength, they break into fragments called fragment or daughter ion which is denoted by M+1. Ions formed are separated in analyzer under the influence of electric and magnetic field and are recorded by the detector to give rise a mass spectrum


The instrument consists of three major components:

1.    Ion Source: For producing gaseous ions from the substance being studied.

2.    Analyzer: For resolving the ions into their characteristics mass components according to their mass-to-charge ratio.

3.    Detector System: For detecting the ions and recording the relative abundance of each of the resolved ionic species.


Mass Spectrometry Assignment


In addition, a sample introduction system is necessary to admit the samples to be studied to the ion source while maintaining the high vacuum requirements (~10-6 to 10-8 mm of mercury) of the technique; and a computer is required to control the instrument, acquire and manipulate data, and compare spectra to reference libraries.  


With all the above components, a mass spectrometer should always perform the following processes:

1.    Produce ions from the sample in the ionization source.

2.    Separate these ions according to their mass-to-charge ratio in the mass analyzer.

3.    Eventually, fragment the selected ions and analyze the fragments in a second analyzer.

4.    Detect the ions emerging from the last analyzer and measure their abundance with the detector that converts the ions into electrical signals.

5.    Process the signals from the detector that are transmitted to the computer and control the instrument using feedback


Ø  Mass spectrometers are sensitive detectors of isotopes based on their masses.

Ø  They are used in carbon dating and other radioactive dating processes.

Ø  The combination of mass spectrometer and a gas chromatograph makes a powerful tool for the detection of trace of trace quantities of toxins or contaminants.

Ø  A number of satellite and spacecraft have mass spectrometer for the identification of small number of particles intercepted in space.

Ø  For example: SOHO satellite uses mass spectrometer to analyze solar wind.

Ø  Mass spectrometer are used for the analysis of residual gases in high vacuum system.


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