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Mass Spectroscopy

Micro Analytical technique- Structure and molecular weight

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MS measures MASS OF INDIVIDUAL IONS produced by fragmentation of the analyte molecule. !Does not involve absorption or emission of electromagnetic radiation !Destructive technique

Mass spectrometer is an instrument which produces charged ions consisting of the parent ion and ionic fragments of the original molecules and sorts these according to their m/e ratio.

! 1912:first mass spectrometer(JJ Thomson)

! 1919:modified form(Aston).

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Mass spectrometry Principle : Mass spectrometry (MS) is based on generating ions in

the gaseous state, separating them according to their mass-to-charge ratio (m/e) and detecting them. !

MS is therefore useful for identification as it can elucidate chemical and structural information about molecules from their molecular weights and distinctive fragmentation patterns. !

MS provides more information about the composition and structure of a compound from less sample than anyother analytical technique.

MS is also very important for the quantitative measurement of atoms or molecules. !

The sensitivity of MS for identifying molecules is in the molar range and for proteins, mass measurement accuracy can be extremely low. !

Instrument ! In general, the operation of a mass spectrometer involves

creating ions in the gaseous phase, separating the ions in space or time based on their mass-to-charge ratio (m/z) and measuring the quantity of ions of each mass-to-charge ratio. !

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Inlet system

Ion source

Mass analyzer Detector

Signal processor

Read out

Vacuum system

Sample

Electric field

Magnetic field

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A mass spectrometer consists of a sample introduction system, an ion source, a mass-selective analyser, an ion detector and a computer.

! Since mass spectrometers create and manipulate

gaseous ions, they operate in a high-vacuum system. !

Sample

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Different according to physical properties Batch inlet system Direct probe inlet Chromatographic & capillary

electrophoretic inlet system.

Sample inlet system

Source The ion source is where the sample of interest is both

ionised with a positive or negative charge and converted into the gas phase.

There are a number of ion sources available: Electron impact Chemical ionisation Electrospray ionisation Atmospheric pressure chemical ionisation Fast atom bombardment Matrix assisted laser desorption ionisation Surface enhanced laser desorption ionisation.

Discriminator The mass analyser (sometimes called mass filter) is the

discriminating element in a mass spectrometer and is where the ions are manipulated and sorted.

There are a number of types of mass analyser and among them are:

Types of mass spectrometers

Single focussing Double focussing Quadrupole Time of flight systems Fourier transformion cyclotron resonance

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Single focusing mass spectrometers