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