Mass spectroscopy

Mass spectroscopy is one of the primary spectroscopic method for molecular analysis of the sample. It is micro analytical technique requiring only a few nano molecules of the sample to obtain characteristics information pertaining to the structure and molecular weight of sample. The mass spectrum of each compound is unique and can be used a chemical fingerprint to characterize the sample.

Basic Principle: Mass spectroscopy is the most accurate method for determining the molecular mass of the compound and its elemental composition.In this technique molecules are bombarded with a beam of energetic electrons. The molecules are ionized and broken up in to many fragments some of which are positive ions.

Mass spectra is used in two general ways:- (1) To prove the identity of two compounds. (2) To establish the structure of a new compounds. The mass spectrum of a compound helps to establish the structure of a new compound in several different ways:- (1) It can give the exact molecular weight. (2) It can give a molecular formula.
Mass spectroscopy

Working principle

Mass spectroscopy deals with the examination of the characteristics fragments (ions) arising from the breakdown of organic molecules. The basic aspect of organic mass spectroscopy consist of bombarding the vapor of an organic compound or sample with a beam of energetic electron accelerated from a filament to an energy of 70ev to form positively charged ions. The energy of electrons breaks the bonds in the molecular ions, which undergoes fragmentation to yield neutral or positively charged species.

This fragmentation may result in the the formation of an even electron ion and radial. The various positive ions thus formed can be accelerated and deflected by magnetic or electric fields. The deflection of ions however, depends on its mass, charge, and velocity. Thus a number of beams each containing ions with the same m/z values are obtained. These beams are then made to strike against a photographic plate where not only appear as separate lines but the intensity of each peak is also recorded.

Instrumentation of mass spectroscopy

Mass spectroscopy

Ionization: The atom is ionized by knocking one or more electron off to give a positive ion (mass spectroscopy always works with positive ions).The particles in the sample are bombarded with a stream of electron to knock or more electron out of the sample particles to make positive ions. These positive ions are persuaded out into the rest of the machine by the ion repealer which is another metal plate carrying a positive charge.

Acceleration: The ions are accelerated so that they all have same kinetic energy. The positive ions are repelled away from the positive ionization chamber and pass through three slits with voltage in the decreasing order. The middle slit carries some intermediate voltage and the final at 0 volts. All the ions are accelerated into a finely focused beam.

Deflection: The ions are then deflected by a magnetic field according to their masses,the lighter the more they are deflected. The amount of deflection also depends on the number of positive charges on the ion the more the ion charged the more it gets deflected. Different ions are deflected by the magnetic field by different amounts.
The amount of deflection depends on: (1) The mass of ion: Lighter ions are deflected more than heavier one. (2) The charge on the ion: Ions with 2 or more positive charges are deflected more than ones with only 1 positive charge.

Detection: The beam of ions passing through the machine is detected electrically. When an ion hits the metal box its charge is neutralized by an electron jumping from the metal on to the ion. That leaves a space amongst the electron in the metal and the electrons in the wire shuffle along to fill it. A flow of electron in the wire is detected as an electron current which can be amplified and recorded the more ions arriving  the greater the current.

Applications

  1. It is used in proteomics.
  2. It is used in metabolomics.
  3. It is also used in environmental analysis.
  4. Pharmaceutical analysis is also done by mass spectroscopy.
  5. It is also used in forensic analysis. 
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