mass Spectroscopy

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Seminar on Instrumentation of Mass Spectroscopy: 

Seminar on Instrumentation of Mass Spectroscopy Presented By :- Saiesh P. Phaldesai Srinivas College Of Pharmacy. Valachil , Mangalore. 1

MASS SPECTROSCOPY: 

MASS SPECTROSCOPY Technique in which the sample is converted into rapidly moving positive ion, which are then separated and characterized. Wont use any type of radiations, only the positively charged ions are get analyzed. So the technique involves conversion of sample in to ions and ion fragments and deals with the study of charged molecules and fragment ions, the relative intensity was obtained from correlating their mass charge ratio . Designated as M/e 2

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MECHANISM If atom or a molecule looses or gains an electron it posses a electrical charge on it. If it looses an electron it attains a positive charge. If it gains an electron it attains negative charge, then the resulting charged molecule or atom is called as ion, process is called as ionization. 3

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It is inconvenient to measure the masses of the molecules. The mass spectrometer is an instrument which measures the mass of the individual molecules. It does not measure the molecular mass directly but it measure the mass to charge ratio of the ions 4

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Ions can be generated by several ways: 1. By electron bombardment. 2. by exposing sample to high intensity laser light. Three main process that occur in the mass spectroscopy are: 1 . Ionization 2. Sorting of ions 3. Detection 5

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INSTRUMENTATION OF MASS SPECTROMETER: 

INSTRUMENTATION OF MASS SPECTROMETER Sample inlet system ( sample handling system). Ion source (electrostatic accelarating chamber). Mass analyzers – Electrostatic and Magnetic analyzers. ( Ion separator tubes) Collectors – Detectors. Data handling ( amplifiers and recorders). Vacuum system. 7

Mass spectrometer.: 

Mass spectrometer. 8

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Sample inlet systems: Permits introduction of sample in to the ion source. Different sampling systems include: Batch inlet system. Direct probe inlet. Introduction of gas samples: Transfer of sample from small containers of known volume. 9

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Liquids: Break off devices. By touching micropipette to sintered glass disk. Hydrodynamic needle injection Solids or Non-volatile liquids. Directly introduced on silica or platinum probe. Being thermaly unstable compounds. 10

1.Ion source: : 

1.Ion source: Chemical ionisation . In this method ionization results from ion molecule chemical interaction. The interaction process involves large amount of reagent gas and a small amount of sample. The reagent ion and sample molecule may react via any of the several modes. Proton exchange . Electron impact source. sample is volatalized in to gas phase. Neutral molecule enter into the ionization chamber , maintained at a pressure of 0.005 torr and at a temperature of 200± 0.25 c. Electrons are emitted from a glowing filament ( thoriated iridium,or carbonized tungsten) electrons emitted from the glowing filament provides sufficient energy to ionize the sample. 11

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Field desorption. In this type anode and cathode are arranged with a very fine gap (0.5 to 2mm) which may serve as a slit. The gaseous sample introduced at the anode points where the electric field is concentrated. The ionisation of the sample takes place by extraction of electrons from the sample by microtips of the anode. Fast atom bombardment. Electro spray ionization . 12

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2.Mass analyzers and ion separator: After passing through the electrostatic slits ions enter in to the analyzers. Separate the ions according to their mass charge ratio. - Electrostatic analyser . - Magnetic analyser . Different types of mass analyzers are: Magnetic deflection or sector mass analyzer . Double focus mass analyzer . Quadrapole mass analyzer . Time of flight mass analyzer. 13

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Magnetic deflection or sector mass analyzer: In this type the homogeneous beam of ions from the slit can be focus by a magnetic field in a shape of a sector. 14

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2. Double focus mass analyzer : Here the ions are analyzed according to their momentum and translational energies. An electrostatic deflection field between the ion source and the mass analyzer. As the ions are passed through the electrostatic sector, they are deflected according to their translational energy. Finally the magnetic sector disperses the ions according to their momentum. 15

1. Nier-johnson double focusing mass spectrometer -It makes use of 900 sectors with intermediate slit : 

1. Nier-johnson double focusing mass spectrometer -It makes use of 90 0 sectors with intermediate slit 2. Mattauh-Herzog double focusing mass spectrometer -This model makes use of an Electric sector with an angle of 31 0 50’. At this angle all ions enter the magnetic field at normal incidence which minimizes the edge effect. The magnetic sector has an angle of 135’, which brings each ionic species to a focus at the far boundary of the field. 16

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3.Quadrapole mass analyzer: The quadrupole consists of four parallel rods. The opposing rods have the same polarity whilst adjacent rods have opposite polarity. Each rod is applied with a DC and an RF voltage. Ions are scanned by varying the DC/ Rf quadrupole voltages . Only ions with the selected mass to charge ratio will have the correct oscillatory pathway in the Rf field. 17

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Quadrapole mass analyzer: 18

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Quadrupole Ion Trap It consists of the doughnut shaped ring electrode and a pair of the end electrodes. A variable radio frequency voltage is applied to the ring electrode, while the two end caps electrodes are grounded. Ions obtained from the chemical or electron impact ionisation is admited through the grid in the upper end cap. Sample is introduced and traped into the cubic cell. 19

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4. Time of flight mass analyzer: As the name indicates the mass spectrum is obtained depending upon the time it took for the ion to reach the detector from accelerating chamber. The energy relation of the paticle remains the same i.e ( zV= ½mv 2 ) , if V and ½mv 2 constant, we get (m/z = 2Vt 2 / L 2 ) 20

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The ions are accelerated and accelerated particles entering the tube having same kinetic energies their velocities in the draft tube must vary inversely with their masses. The lighter particles arriving at the collector earlier than heavier. t = L/v ------- time of flight equation. t - time taken for the ion to pass through a drift tube. v - velocity of the charged particle. l - length of the tube. 21

Time of flight mass analyzer: 

Time of flight mass analyzer Ion source reflector flight tube detector same m/z, but higher initial kinetic energy than 20 kV 23 kV t (m/z) Good resolution ! Mass accuracy ± 10-50 ppm Sensitivity (low femto-mole) I 22

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3. Ion collecting systems or detectors: Ions are amplified and recorded. various detectors used are- Faraday cup collector. Electron multiplier. Ion sensitive photographic plates. 23

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1.Faraday cup collector: Simple and effective means of monitoring ion current. When sufficient amount of sample is available the measurement can be done by collecting them in single Faraday cup and scanning for different masses charge values. Advantages:- Current as low as 10 -5 A may be detected. Disadvantage It needs high impedance amplifier , which limits the speed at which spectrum can be scanned. 24

Faraday cup collector: 

Faraday cup collector 25

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2. Electron multiplier: When the amount of sample available is small, the ion current produced is such a low current cannot be measured directly with a Faraday cup and further amplification is carried out by the secondary electron multiplier. 26

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3. Ion sensitive photographic plates: Here the ions directly expose a photographic film. This type of detectors used in mass analyzers. Which disperse ions according to their mass to charge ratio. The ion sensitive photographic plate integrate the ions and record them. This detector provides greater resolution and highest sensitivity. 27

Ion sensitive photographic plates: : 

Ion sensitive photographic plates: 28

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The vaccum system: Whole instrument is kept under high vacuum conditions 10 -6 to 10 -7 . Two types of pump systems are used- Backing rotary pumps. Oil diffusion pump. 29

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Data handling: Data are digitalized and collected on magnetic tape or stored in a memory of computer. Recorders: Multichannel ultraviolet recorder. Pens, tape recorders, oscillators other data collecting systems are used as recording devices. 30

References:: 

References: Gurudeep R. Chatwal, Sham K. Anand, ‘Instrumental methods of chemical analysis’ P.No: 2.278-2.283. Dr. B.K. Sharma. Spectroscopy. P.No: 862-864 Skoog , D. A.; Holler, F. J.; Nieman, T. A., 'Principles of Instrumental Analysis', fifth edition, P. no: 258-261, 514-521 http://masspec.scripps.edu/MSHistory/whatisms.php www.Google.com 31