1.5 Atomic Absorption Spectroscopy

• When atoms absorb radiation, their electrons get excited and gain energy to transition to higher energy levels, altering their electron configuration temporarily. When the electrons fall back to their original ground states, the energy is released as specific wavelengths of colour. 
• 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 [Normal]
• Copper:1s2 2s2 2p6 3s2 3p6 3d10 4s1
• Chromium: 1s2 2s2 2p6 3s2 3p6 3d5 4s1
• A has a unique energy profile. The light produced at the lamp by heating up pure A has a specific wavelength absorbed by exciting electrons. Because other elements’ electrons have different energy profiles, they cannot absorb the light and will not affect the measurement of concentration of A’s ions. 
• Atomic Absorption Spectroscopy Spectrum

  1. The sample in an aqueous solution is vapourised causing the atoms to freely dissociate via a gas flame of the nebulizer 
  2. Light from a hollow cathode lamp is passed through the sample, which is made of the same metal as the metal ion present in the sample. This is because only its ions can absorb light of specific wavelengths emitted by the lamp. 
• Atomic Absorption Spectroscopy Spectrum

  3. A monochromator is used to isolate a single wavelength line that is unique to the element.

  4. The single wavelength of light is passed into a detector and is analysed to see how much has been absorbed. The higher the concentration of the metal ion in the sample, the greater the amount of light absorbed.
• Construction of Calibration Graphs:

  1. A sample of water is placed in AAS machine and its absorbance is recorded which should be 0 otherwise a systematic error is present 
  2. A minimum of 3 samples of a known concentration of the metal ion is placed in AAS and its absorbances are recorded
  3. Graph is constructed where absorbance is on the y-axis and concentration on the x-axis  
• It can be seen with the calcium ion electron configuration that its electron has transitioned to a higher energy level of 4s rather than the more stable 3p. This indicates a specific wavelength of light has been absorbed by the electron to excite them to the higher energy level.