What is Mass Spectrometry?

Mass spectrometry is not a true spectroscopic technique because absorption of electromagnetic energy is not involved in any way.

Mass spectrometry is use to characterized organic molecule in two principal ways:

        I.            To measure exact molecular weight, and by this, exact molecular formula can be determined.

      II.            To indicate the point at which molecule prefers to fragment; from this, the presence of certain structural units in the compound can be recognized.

A Mass spectrum is a presentation of the masses of the positively charged fragments versus their relative concentrations. The most intense peak in the spectrum, called the ‘Base peak’ is assigned value of 100%, and the intensity of other peaks, are reported as percentage of the base peak.

The commonly used technique in mass spectrometry is ‘Electron Impact’. In this mode spectrometer bombards molecules in the vapor phase with a high energy electron beam and record the result of electron impact as a spectrum of positive ions separated on the bases of mass/charge (m/z).  On electron impact, the molecules are energized sufficiently to eject an electron, thus produces molecular ion M^+.which further fragments to more daughter ions.

The molecular ion though it may be of low abundance gives highly useful information about the identity of an organic compound. Fragmentation pattern that is the break-up process of the molecular ion into smaller ions gives further information about the structure of compound.

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Electromagnetic Spectrum

Electromagnetic radiation is radiant energy having the properties of both particles and

waves. A continuum of different types of electromagnetic radiation—each type associated

with a particular energy range which constitutes the electromagnetic spectrum.

Visible light is the type of electromagnetic radiation with which we are most familiar, but

it represents only a fraction of the range of the entire electromagnetic spectrum.

X-rays and radio waves are other types of familiar electromagnetic radiation.

The electromagnetic spectrum is made up of the following components:

• Cosmic rays, which consist of radiation discharged by the sun, have the highest energy, the highest frequencies, and the shortest wavelengths.

• (gamma rays) are emitted from the nuclei of certain radioactive elements and, because of their high energy, can severely damage biological organisms.

• X-rays, somewhat lower in energy than are less harmful, except in high doses. Low-dose X-rays are used to examine the internal structure of organisms.

• Ultraviolet (UV) light is responsible for sunburns, and repeated exposure can cause skin cancer by damaging DNA molecules in skin cells.

• Visible light is the electromagnetic radiation we see.

• We feel infrared radiation as heat.

• We cook with microwaves and use them in radar.

• Radio waves have the lowest energy (lowest frequency). We use them for radio and television communication, digital imaging, remote controls, and wireless linkages for laptop computers. Radio waves are also used in NMR spectroscopy and in magnetic resonance imaging (MRI).

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