Question

In a routine atomic absorption spectrometry determination of metal ions in blood), an analyst needs to obtain the blood-level concentration of lithium in patients taking lithium carbonate, Li₂CO₃, as a treatment for mental disorders. What specific type of light source is required for the AAS analysis of the lithium content of the blood samples?

Answer 1

Atomic absorption spectrometry is a method which we can use to measure the concentration of metallic elements. It is an analytical method which uses a light source.

Every element can absorb a specific wavelength of light. On absorbing the light, the intensity of the emitted light is reduced. Therefore there is a change in the wavelength of light emitted from the light source and the light after absorption. This change in wavelength is measured and from this we can determine the concentration of the element.

In AAS, the element whose concentration is to be measured is dissociated from its chemical bonds and is placed in its ground state (no exited electrons). At this state, the atom can absorb radiation at a bandwidth corresponding to its line spectrum.

So if Lithium is to be analyzed, we use a hollow cathode lamp with the cathode being Lithium as the light source. This lamp emits light of wavelength 670.8 nm. This light is then absorbed by the ground state Lithium atoms resulting in a decrease in the intensity of the light.

The hollow cathode lamp consists of a cathode and an anode. It is sealed and filled with an inert gas. A high voltage is applied across the anode and the cathode which excites the inert gas which results in the gas ions striking the cathode. This excites the atoms in the cathode and a beam of light is emitted.