Mass Spectrometer
As spectrum is the intensity of light vs. wavelength of light (Fig. 1). The mass spectrum is the intensity of isotope vs. the mass of the isotope (Fig. 2). Mass Spectrometer is the instrument we use to get the mass spectrum.
Structure and Working Principle
1
Ion Source: To get the mass spectrum, we first need to get the ion mode of isotope. We use methods like high temperature, plasma etc. to ionize the isotope. After the ions are got, those ions will be accelerated by 10 thousands high voltage and fly into the flying tube of the mass spectrometer.
2
Mass Analyzer : When ions fly into the magnet field, ions will sense a force vertical to their velocity, this force will let those ions begin to make a turn. The radius of flying path of those ions is related to mass and electric charge of the ions. When the electric charge of ions is the same, the radius of flying path is determined by the mass of ion only. When ions fly into the magnet field, the heavier ions will have larger radius of flying path and the lighter ions will have smaller radius of flying path, so when ions fly into the magnetic field, isotope ions of different mass will be separated, each mass will follow their only flying path.
In the formula we can see the radius of flying path is direct proportion to the square root of the mass – electric charge ratio, so if the electric charge of each ion is the same, in the same accelerate high voltage and magnetic field, the radius of flying path is determined by the mass of ion only.
r: Radius of Flying Path
V: Accelerate High Voltage
B: Intensity of Magnetic Field
m: Mass of Ion
q: Electric Charge of Ion
3
Detector : Detector is the last stop of the isotope ions. When ions fly into detector, detector will get an electron from the wire connected to it to neutralize the ion. Because each ion need an electron to neutralize, so in the same time the more ions need more electrons, this means the current in the wire is higher, so we can know the higher current the detector need means the higher intensity of the isotope ions the detector got.
Application of Mass Spectrometer
Mass spectrometers have a wide range of applications in biology, chemistry, and environmental science. In earth sciences, we generally use it to measure the isotopic ratios of radioactive elements.