mass spectroscopy 2
DESCRIPTION
spectroscopyTRANSCRIPT
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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
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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.
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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
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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.
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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:
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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