Motion Of Charges In The Presence of Electric and Magnetic Fields - Mass Spectrometer

  • Introduction to Mass Spectrometer
    • Device used to measure the masses of individual atoms and molecules
    • Principle based on deflection of charged particles in electric and magnetic fields
  • Components of a Mass Spectrometer
    • Ionization source
    • Accelerator
    • Analyzer
    • Detector
  • Ionization Source
    • Converts sample molecules into ions
    • Common methods: electron impact, electrospray ionization, laser desorption/ionization
  • Accelerator
    • Accelerates ions to high speeds
    • Common methods: electric fields, magnetic fields, both combined
  • Analyzer
    • Separates ions based on their mass-to-charge ratio (m/z)
    • Common methods: magnetic sector, quadrupole, time-of-flight (TOF)
  • Detector
    • Measures the number of ions reaching the detector
    • Common types: electron multiplier, photomultiplier, Faraday cup
  • Working Principle of Mass Spectrometer
    • Sample ionization
    • Ion acceleration
    • Ion deflection in magnetic field
    • Ion separation in analyzer
    • Ion detection and measurement
  • Calculation of m/z ratio
    • Mass-to-charge ratio (m/z) = mass of ion (m) / charge of ion (z)
    • Example: Calculate m/z ratio for an ion with mass 14 amu and charge +2
  • Applications of Mass Spectrometry
    • Drug discovery and development
    • Environmental analysis
    • Forensic sciences
    • Proteomics and metabolomics
  • Advantages of Mass Spectrometry
    • High accuracy and precision
    • Wide range of analytes can be detected
    • Non-destructive technique for sample analysis

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  1. Principle of Electric Fields
  • Electric fields exert forces on charged particles
  • Force experienced by a charged particle in an electric field is given by the equation: F = qE
  • Here, F represents the force on the particle, q represents the charge of the particle, and E represents the electric field strength
  1. Principle of Magnetic Fields
  • Magnetic fields exert forces on moving charged particles
  • Force experienced by a charged particle moving in a magnetic field is given by the equation: F = qvBsinθ
  • Here, F represents the force on the particle, q represents the charge of the particle, v represents the velocity of the particle, B represents the magnetic field strength, and θ represents the angle between the velocity and the magnetic field direction
  1. Combined Electric and Magnetic Fields
  • When charged particles are subjected to both electric and magnetic fields simultaneously, they experience a combined force
  • The combined force is given by the equation: F = q(E + vBsinθ)
  • The motion of the charged particle depends on the relative magnitudes and directions of the electric and magnetic fields
  1. Cyclotron Motion
  • Cyclotron motion is a specific type of motion that occurs when charged particles move in a magnetic field
  • During cyclotron motion, the charged particle moves in a circular path perpendicular to the magnetic field direction
  • The radius of the circular path can be determined by the equation: r = mv / (qB)
  • Here, r represents the radius, m represents the mass of the particle, v represents the velocity of the particle, q represents the charge of the particle, and B represents the magnetic field strength
  1. Hall Effect
  • The Hall effect refers to the phenomenon of a voltage difference appearing across a conductor carrying a current in the presence of a magnetic field perpendicular to the current
  • The voltage difference is given by the equation: V = BIL / ne
  • Here, V represents the voltage difference, B represents the magnetic field strength, I represents the current, L represents the length of the conductor, n represents the number density of charge carriers, and e represents the charge of an electron
  1. Velocity Selector
  • A velocity selector is a device used to select charged particles of a specific velocity from a mixture of particles
  • It consists of crossed electric and magnetic fields such that only particles with a specific velocity pass through the crossed fields
  • The velocity selector works on the principle of balancing the electric and magnetic forces experienced by the particles
  1. Charged Particle Deflection
  • When a charged particle travels through a region with both electric and magnetic fields, it experiences deflection
  • The direction of deflection depends on the relative magnitudes and orientations of the electric and magnetic fields
  • The deflection can be used to determine the charge-to-mass ratio (q/m) of the particles
  1. Charge-to-Mass Ratio Calculation
  • The charge-to-mass ratio (q/m) of a charged particle can be determined by measuring its deflection in an electric and magnetic field setup
  • The equation used to calculate the charge-to-mass ratio is: q/m = 2V / (r^2B^2)
  • Here, q represents the charge of the particle, m represents the mass of the particle, V represents the accelerating voltage, r represents the radius of the circular path, and B represents the magnetic field strength
  1. Cathode Ray Tube (CRT)
  • A cathode ray tube is a vacuum tube device used to display images
  • It consists of a cathode emitting a beam of electrons, which is deflected by applying electric and magnetic fields to create the desired image
  • CRTs were commonly used in old television sets and computer monitors
  1. Mass Spectrometry in Everyday Life
  • Mass spectrometry has applications in various fields of everyday life
  • It is used in food safety analysis to detect contaminants and ensure quality
  • Mass spectrometry is employed in drug testing to detect the presence of illegal substances in athletes
  • Environmental monitoring utilizes mass spectrometry to identify pollutants in air, water, and soil
  • Forensics relies on mass spectrometry for identifying materials, analyzing crime scene evidence, and identifying drugs in biological samples.