Spectroscopy Techniques Chemistry Tutorial

Key Concepts

• Spectroscopy is the study of the interactions between radiant energy and matter.
• Spectroscopy can be used to determine the:

  (a) presence or absence of an element such as a metal
  (Flame Tests and emission spectroscopy)

  (b) amount of an element present
  (colorimetry, Atomic Absorption Spectroscopy (AAS), UV-Visible Spectroscopy)

  (c) structure of a compound
  (mass spectroscopy, ¹H nuclear magnetic resonance spectroscopy, ¹³C nuclear magnetic resonance spectroscopy, infrared spectroscopy, UV-visible spectroscopy)

• A spectroscopic technique may rely on either:

  (a) emission of energy from the substance being investigated
  (Flame Tests and emission spectroscopy)

  (b) absorption of energy by the substance being investigated
  (colorimetry, Atomic Absorption Spectroscopy (AAS), UV-Visible Spectroscopy)

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Comparison of Spectroscopy Techniques used to Determine Presence and/or Amount of Substance

Type: Flame Tests
Features	Uses
inexpensive fast, but some colours may be masked by others making it unreliable qualitative technique limited application as many common metals (e.g., Al & Mg) do not colour a flame a type of emission spectroscopy which can be observed by the naked eye or by using a spectroscope to see a series of bright lines	Identification of metals in some salts Li+       crimson Na+     yellow K+       lilac Ca2+   brick red Sr2+   scarlet Ba2+   green Cu2+   green-blue
Type: Colorimetry
Features	Uses
relatively inexpensive fast, requiring a set of standard solutions qualitative & quantitative a type of absorption spectroscopy limited to coloured solutions or compounds	copper(II) sulfate in garden sprays iron(III) concentration using KSCN to form the coloured Fe(CNS)2+ complex coloured solutions such as food colourings
wavelength of light is selected for maximum absorbance & a calibration curve is constructed of absorbance versus concentration
Type: Atomic Absorption Spectroscopy (AAS)
Features	Uses
expensive fast, requiring a set of standard solutions quantitative a type of absorption spectroscopy that can be used for all metals and metalloids (semi-metals)	mercury in shellfish lead in soil samples trace metals in mineral waters
correct hollow cathode tube selected & a calibration curve constructed of absorbance versus concentration. (solutions may have to be diluted)
Type: UV-Visible Spectroscopy
Features	Uses
expensive fast, requiring a set of standard solutions qualitative & quantitative a type of absorption spectroscopy limited to coloured solutions or compounds	concentration of some coloured pharmaceuticals in blood serum concentration of metal ions using coloured complexes concentration of food colourings
wavelength of light selected for maximum absorbance and a calibration curve constructed of absorbance versus concentration