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Instrumental Chemistry

Instrumental Chemistry. Chapter 11 Atomic Mass Spectrometry. Atomic mass. The mass of a single atom, usually expressed in atomic mass units (amu) Most of the mass of an atom is concentrated in the protons and neutrons contained in the nucleus

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Instrumental Chemistry

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  1. Instrumental Chemistry Chapter 11 Atomic Mass Spectrometry

  2. Atomic mass • The mass of a single atom, usually expressed in atomic mass units (amu) • Most of the mass of an atom is concentrated in the protons and neutrons contained in the nucleus • Each proton or neutron weighs about 1 amu, and thus the atomic mass is always very close to the mass number (total number of protons and neutrons in the nucleus)

  3. Mass Spectrometers • Mass spectrometers use the difference in mass-to-charge ratio (m/e) of ionized atoms or molecules to separate them from each other • In general a mass spectrometer consists of an ion source, a mass-selective analyzer, and an ion detector

  4. Diagram of a Mass Spectrometer

  5. Stage 1: Ionization • The atom is ionized by knocking one or more electrons off to give a positive ion • These positive ions are persuaded out into the rest of the machine by the ion repeller which is another metal plate carrying a slight positive charge

  6. Ionization (cont.)

  7. Stage 2: Acceleration • The ions are accelerated so that they all have the same kinetic energy • All the ions are accelerated into a finely focused beam

  8. Acceleration (cont.)

  9. Stage 3: Deflection • The ions are then deflected by a magnetic field according to their masses • The lighter they are, the more they are deflected • The more the ion is charged, the more it gets deflected

  10. Deflection (cont.)

  11. Stage 4: Detection • The beam of ions passing through the machine is detected electrically • When an ion hits the metal box, its charge is neutralized by an electron jumping from the metal on to the ion • That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it

  12. Detection (cont.)

  13. Fourier-Transform MS

  14. Magnetic-sector MS

  15. Quadrupole MS

  16. Time-of-flight MS

  17. ICP-MS • Inductively Coupled Plasma Mass Spectrometry • In ICP-MS, the plasma is formed from Argon gas • Plasma is defined as a gas consisting of ions, electrons, and neutral particles

  18. SSMS • Spark Source Mass Spectrometry • Semi-quantitative trace element technique for the analysis of solids and liquid materials • Advantages include total simultaneous elemental coverage, low detection limits, semi-quantitative accuracy (+2-3x), and high resolution capabilities to eliminate many spectral interferences

  19. GDMS • Glow-Discharge Mass Spectrometry • Analytical technique for the bulk elemental analysis of inorganic solid samples • The most comprehensive and sensitive technique available for the analysis of solids

  20. Glow Discharge Ion Source

  21. Useful Websites Dealing With Mass Spectrometry • http://www.anachem.umu.se/jumpstation.htm • http://userwww.service.emory.edu/~kmurray/mslist.html • http://www.chemcenter/org • http://www.sciencemag.org • http://reference.allrefer.com/encyclopedia/A/atomMas.html • http://www.webref.org/geology/a/atomic_mass.htm • http://www.chemguide.co.uk/analysis/masspec/howitworks.html • http://www.northernanalyticallab.com/tech2.htm • http://www.shivatec.com/new/gdmsdesc.php4

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