Atomic Absorption Spectroscopy (AAS)

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Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements    

  • Spectroscopy: The study of the interaction of electromagnetic radiation with matter.
  • When vaporised, different elements absorb light of specific frequencies.
  • Atomic absorption spectroscopy (AAS): A technique used to identify the presence and concentration of substances by analysing the spectrum produced when a substance is vaporised and absorbs certain frequencies of light.
  • AAS is used particularly for detecting the concentrations of metal ions in solutions.
  • AAS is performed using an atomic absorption spectrometer.

Schematic diagram of an atomic absorption spectrometer


  • To determine the concentration of a certain metal ion in a sample, the following steps occur within an atomic absorption spectrometer:
    • A hollow cathode lamp, with the cathode made of the metal to be tested for, emits light of a certain frequency.
    • The light produced by the lamp is passed through the sample to be tested vaporised in a flame.
    • The degree of light absorption is proportional to the concentration of the metal in the sample.
    • The intensity of the light that passes through the flame is measured by a photomultiplier tube.
    • By comparing the intensity with that produced from a control sample containing none of the metal ions being tested for, the degree of absorption, or absorbance, can be determined.
    • The absorbance is then compared to that of a series of diluted standard solutions in order to determine the concentration.
    • This involves the use of a calibration graph.

General layout of a calibration graph

    • The standard solutions should produce a straight-line graph.
    • The absorbance recorded for the sample being tested can be matched with a concentration using the graph.
  • Trace element: Also known as a micronutrient, an element required in minute amounts for normal growth of organisms.
  • Trace elements work in organisms by helping enzymes to function.
  • The concentration of trace elements in animals and plants is normally in the range of 1 to 100 parts per million.
  • Before the development of AAS in the 1950s, commonly used analytical methods were not sufficiently sensitive to detect the low concentrations of these elements, and their presence went unnoticed.
  • When scientist began to use AAS on organisms and soils, the existence of these trace elements were first recognised.
  • AAS has also been used to help demonstrate both the necessity and function of these elements.
  • Thus, AAS has had a great impact on scientific understanding of the effects of trace elements.
  • In the case of the ill health of an organism, AAS can be used to detect whether required trace elements are present in sufficient quantities in the organism and its environment.
  • If a trace element deficiency is observed, then it can be rectified by providing the organism with that particular nutrient.
  • This is especially useful in the field of agriculture, where specific practical applications of AAS have included:
    • The discovery of a cobalt deficiency in seemingly good pastureland in coastal southwestern Australia where animal health could not be maintained.
    • The discovery of a molybdenum deficiency in the soils of arid parts of Victoria where legume crops could not be supported.