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Atomic Absorption Spectrometry

 Atomic Absorption Spectrometry is an absorption spectroscopic technique in which radiation of a particular frequency from a source is absorbed by non-excited neutral gaseous atoms  generated in an atomizer in their ground state.
  • The light is absorbed in the UV-visible region and makes transitions to higher electronic energy levels.
  • The amount  of light absorbed is quantified and this amount of absorption helps in determining the analyte concentration. (It follows Beer's Law)
  • The concentration is measured by drawing a calibration curve after calibrating instrument with a standard of known concentration.


Factors affecting  the amount of light absorbed

  1. Length of path transversed
  2. Concentration of absorbing atoms in the vapour state.
The diagrammatic representation of Atomic Absorption Spectrometer are shown in the below diagram:



 Components Used in Atomic Absorbance Spectrometer:

1. Hollow Cathode Lamp: Acts as source of radiation 

  • It is a sharp line radiation source.
  • It has a Pyrex body with end window of quartz
  • The lamp is evacuated and filled with an inert gas usually argon or neon.
  • The lamp operates at current below 30 mA and voltages upto 400V.
  • The cathode is bombarded with positively charged inert gas ions accelerated by electrical potential.
  • On collision of positively charged inert gas ions with cathode surface (usually metals or metalloids), the atoms of cathode are moved to excited electronic state which emit radiations 

2. Nebulizer: 

It is a small machine which converts liquid sample into the fine must/spray.
The sample is introduced through an orifice to mix with a high velocity gas jet (usually an oxidant) thereby converting it into fine spray.

3. Atomizer: 
Flame mostly acts as atomizer isolating the neutral atoms in their ground state.

Absorption of Radiation source by these neutral atoms in ground state:
  1. The radiation from hollow cathode lamp strikes these neutral atoms in ground state, converting them into higher electronic energy levels.
  2. The transition between the ground state and the first excited state is known as first absorbance line (line of strongest absorptivity).
  3. The shape of the spectral line emitted by the source is a critical parameter in Atomic Absorbance Spectrometry (AAS).
  4. For quantitative measurements, the width of the line emitted by the narrow light source must be smaller than the width of absorption line of analyte in the flame.
  5. Absorbance is determined by the difference between the radiant power of the resonance line in presence and absence of the analyte atoms in flame.

  • Important question: Why only metals and metalloids are detected using atomic absorbance spectrometers (using UV and visible light) but not the non- metals?

  • For most of metal and metalloids, the first absorbance line falls above 200 nm but below 185 nm for non - metals. So, only metals and metalloids are detected using atomic absorbance spectrometers (using UV and visible light) but not the non- metals.


4. Monochromators: Isolate the Resonance lines 


5. Detector: Measure the power of transmitted radiation.


Applications of Atomic Absorption Spectrometry:

1. Water Analysis: for determining the presence and quantification of Ca, Mg, Fe, Si, Al and Ba in water samples.

2. Food Analysis.

3. Soil Analysis.

4. Analysis of additives in lubricating oils and greases.

5. Analysis of animal feedstuffs.

6. Clinic analysis of blood samples (whole blood, plasma, serum, Ca, Mg, Li, Na, K, Fe).


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