Mass Spectrometer

The mass of atoms, molecules and fragments can be measured using a mass spectrometer.

1) All the air in the spectrometer is first pumped out.

2) A sample - element/compound - gaseous form - injected - MS + is bombarded with high-energy electrons - electron gun. If substance solid - heated too produce sufficient number of gaseous particles. Energy from the bombarding electrons strips electrons from the atoms/molecules, forming positive ions:

• A(g) + energy --> A+(g) + e-    where A represents an atom
• M(g) + energy --> M+(g) + e-   where M represents a molecule

+ions formed from molecules can fragment into 2 or more particles, 1 + and other neutral e.g. chlorine: Cl2(g) --> Cl2+(g) --> Cl+(g) + Cl(g) and from ethanol: C2H5OH(g) --> C2H5OH+(g) --> C2H5+(g) + OH(g) and C2H5OH(g) --> C2H5OH+(g) --> C2H5+(g) + OH(g)

3) +ions accelerated by high electric potential, pass through slits + emerge as a parallel beam of ions. All ions have same energy so those of a particular mass have the same speed

4) Ions - deflected by powerful magnetic feild - those with greater mass: deflected less than those of a smaller mass. Ions sorted according to mass. Angle deflected depends upon the strength of magnetic feild and the mass-to-charge ratio (m/e) of the ion.

5) Ions of lowest mass - deflected first. Magnetic feild gradually increased + ions of greater mass are then deflected. Detector couple to computer and calculates the m/e ratio of each +ion and relative abundance compared with the most abundant particle. Converted to % for each +ion

• bombardment - by high energy electons to create +ion
• acceleration - of +ions by an electric potential
• deflection - of +ions by a magnetic feild  
• detection - of +ions

B . A . D . D = BIG APPLES DON'T DIE

Data can be obtained from mass spect od calculate RAM of an element

WORK IT OUT:

R.A.M = (m/e x %) + (m/e x %) = anwser ---> anwser/100 == R.A.M

• Detection of drugs in urine samples

• In the pharmaceutical industry

• Carbon-14 dating