Mass Spectrometry (Part-II) Electrostatic Acceleration System

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S.O.s. in environmental chemistry Jiwaji university, gwalior Presentation on:- Mass Spectrometry (part-II) Electrostatic Acceleration System:- 1) The positive ions formed in the ionisation chamber are withdrawn by the electric field which exists between the first accelerator plate and the second repeller plate. 2) A strong electrostatic field between accelerator and repeller plate accelerates the ions of masses m1 m2 m3... to their final velocities. 3) The ions which escape through slit having velocities and kinetic energies give. 2 2 2 eV=1/2m1v1 =1/2m2v2 =1/2m3v3 ...... Vacuum system:- 1) A high vacuum is to be maintained. 2) The inlet system is generally maintained at 0.015 torr, the ion source at 10-15 torr and analyzer tube at 10-7 torr or as low as possible. 3) Oil diffusion and mercury diffusion pumps are commonly used in different types of combination Mass analyzers:- 1) Separate ions based on their mass-to-charge ratio (m/z) 2) Operate under high vacuum (keeps ions from bumping into gas molecules) 3) Actually measure mass-to-charge ratio of ions (m/z) Types of mass analyzers:- 1) Quadrupole mass analyzer 2) Time of flight analyzer (TOF) 3) Magnetic sector mass analyzer a) Single focusing b) Double focusing 4) Quadrupole ion trap mass analyzer Quadrupole mass analyzer:- 1) It consists of 4 voltage carrying rods. 2) The ions are pass from one end to another end 3) During this apply the radiofrequency and voltage complex oscillations will takes place. 4) Here the single positive charge ions shows the stable oscillation and the remaining the shows the unstable oscillations Magnetic Sector Mass Analyzer:- In magnetic sector analyzers ions are accelerated through a flight tube, where the ions are separated by charge to mass ratios. m/z = B2 R 2 / 2V Time of flight analyzer:- Detector:- 1) Electron multiplier:- Electron multipliers use a process known as secondary electron emission. 2) Faraday cup:- A Faraday cup is a metal (conductive) cup designed to catch charged particle in vacuum. The mass spectrometer:- Mass Spectrum:- A plot of the relative abundance of ions versus their mass-to-charge ratio (m/z). Derived from Fragment Ions molecular ion or higher weight fragments molecular ion Unit mass spacing Mass, as m/z. Z is the charge, and for doubly charged ions (often seen in macromolecules), masses show up at half their proper value Mass spectrum of propane:- Applications:- 1) Pharmaceutical: drug discovery, combinatorial chemistry, pharmacokinetics, drug metabolism. 2) Clinical: neonatal screening, haemoglobin analysis, drug testing. 3) Environmental: PAHs, PCBs, water quality, food contamination. 4) Geological: oil composition. 4) Biotechnology: the analysis of proteins, peptides..

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