Atomic Absorption Spectroscopy (AAS)

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.

Easychem - Atomic Absorption Spectroscopy (AAS)