Chemical Analysis AAS Heavy Metals

Atomic Absorption Spectroscopy (AAS)

Reference:

Pockets Encyclopedia, 1997, Bob Gordon, Helen Parker, Dorling Kindersley, London, UK

Principles of Instrumental Analysis, 2004, Teaching Team of PIA Dip. Chem.Engn., Temasek Polytechnic Applied Science School, Singapore

AAS is a method to detect heavy metals, such as Mercury, Arsenic and Etc. It is also used to detect other metals.

General Principles of AAS.

Light Source (Cathode Lamp) of specific wavelength absorbed by heavy metal is emitted
Sample (heavy metals) gets vaporised and atomised using flame
Atomised Heavy Metal absorbed light wave
Monochromator Separates the light spectrum
Detector detects the intensity of light spectrum that is of interest
Electrical signal converts to chromatogram

1. Explanation on how light source emits specific wavelength that the hevy metal will absorb

Definition of light:
· A fast moving form of energy
Electromagnetic Spectrum

Occurrence of light:

Atoms have many orbital
Each level of orbital represents an energy level
The outer most shell have the highest energy level
Inner most shell have the least energy level
When electrons move from a lower energy level to a higher energy level and jumps back to the lower level of energy, it will emit photons, i.e. light

Occurrence of specific wavelength in Cathode lamp

The Lamp contains a Anode (+ terminal) and Cathode (- terminal)
When a electrical current pass through Anode will be highly + charged
Cathode will be highly – charged
Metal atoms’ electron (-) will lose it electron to the Anode (Process of ionisation)
I.E. electron move from lower energy level to higher energy level
When electrical current switched off, electrons will move from a higher energy level to a lower energy level
Therefore photons (of specific metal wavelength) is emitted
Absorption of Energy

· When metals are burnt by flame, energy is imparted, the metal will ionise or atomised
· When electrons from a higher energy level move to a lower energy level, photons is emitted
· When electrons move from a lower energy level to higher energy level, photons is absorbed
· Specific wavelength of light ( e.g Hg) is emitted
· With that wavelength of light, only Hg will absorbed it
· Therefore the amount of absorbance of light from the known amount of emitted light is correlated with the amount of metals present