Working Principle of Atomic Absorption Spectroscopy (AAS)

Atomic absorption spectroscopy (AAS) determines the presence of metals in liquid samples. Metals include Fe, Cu, Al, Pb, Ca, Zn, Cd and many more. It also measures concentration of metals in the sample. Typical concentration range in the low mg/L. In their elemental form, metals will absorb ultraviolet light when they are excited by heat. Each metal has characteristic wavelength that will be absorbed. The AAS instrument looks for a particular metal by focusing a beam of ultraviolet (UV) light at a specific wavelength through a flame and eventually detected by a detector.The sample of interest is aspirated into the flame. If that metal is present in the sample, it will absorb some of the light, thus reducing its intensity. The instrument measures the change in intensity which is converted into corresponding absorbance by computer software. As concentration goes up, absorption goes up. The analyst can construct calibration curve by running standards of various concentration on AAS and observing absorbance.

Principle: When under normal conditions, atom exist in their most stable state (ground state). Although, we cannot measure pressure energy at ground state, we can measure changes to its energy relative to its ground state.
Certain process can change energy state of atom. For example; adding thermal energy can cause atom to higher energy state. This change in energy is written as E. Transition from ground state to the first excited state requires some form of energy input. This energy is absorbed by the atom. When this energy absorption takes place in place of UV light, some of that light will be absorbed giving spectra. This UV absorption occurs at specific wavelength. Each element in periodic table will have specific E that will absorb specific wavelength of light.

In AAS, sample is aspirated is aspirated into a flame into a flame using nebulizer. This flame is aligned up in the beam of light of appropriate wavelength. The flame (heat) causes atom present in sample to undergo a transition from ground state to excited state. During transition, they absorb some of the light from beam. The more the concentrated solution, the more light energy is absorbed. The light beam is generated by lamp that is specific for target metal. When some of the light is absorbed by metal, intensity is reduced. Dictator records that reduction as an absorption which is converted to graphic form by data processor.



About Author

Name : Pratiksha Shrestha

Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.