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  Section: Practical Skills in Chemistry » Instrumental techniques
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Basic spectroscopy

Instrumental techniques
  Basic spectroscopy
    Introduction to spectroscopy
    UV Ivisible spectrophotometry
    Fluorescence spectrophotometry
    Phosphorescence and luminescence
    Atomic spectroscopy
  Atomic spectroscopy
    Atomic Absorption Spectroscopy
    Atomic Emission Spectroscopy
    Inductively coupled plasma
    Decomposition techniques for solid inorganic samples
  Infrared spectroscopy
  Nuclear magnetic resonance spectrometry
    1H-NMR spectra
    13C-NMR spectra
  Mass spectrometry
    Interfacing mass spectrometry
  Chromatography ~ introduction
    The chromatogram
  Gas and liquid chromatography
    Gas chromatography
    Liquid chromatography
    High-performance liquid chromatography
    Interpreting chromatograms
    Optimizing chromatographic separations
    Quantitative analysis
    The supporting medium
    Capillary electrophoresis
    Capillary zone electrophoresis (CZE)
    Micellar electrokinetic chromatography (MEKC)
  Electroanalytical techniques
    Potentiometry and ion-selective electrodes
    Voltammetric methods
    Oxygen electrodes
    Coulometric methods
    Cyclic voltammetry
  Radioactive isotopes and their uses
    Radioactive decay
    Measuring radioactivity
    Chemical applications for radioactive isotopes
    Working practices when using radioactive isotopes
  Thermal analysis

Light is most strictly defined as that part of the spectrum of electromagnetic radiation detected by the human eye. However, the term is also applied to radiation just outside that visible range, e.g. ultraviolet (UV) and infrared (IR) 'light'. Electromagnetic radiation is emitted by the sun and by other sources (e.g. an incandescent lamp) and the electromagnetic spectrum is a broad band of radiation, ranging from cosmic rays to radio waves (Fig. 26.1). Most chemical experiments involve measurements within the UV, visible and IR regions (generally, within the wavelength range 200-1000 nm).

Radiation has the characteristics of a particle and of a vibrating wave, travelling in discrete particulate units, or 'packets', termed photons. A quantum is the amount of energy contained within a single photon (it is important not to confuse these two terms, although they are sometimes used interchangeably in the literature). In some circumstances, it is appropriate to measure light in terms of the number of photons, usually expressed directly in moles (6.02 × 1023 photons = 1 mol). Alternatively, the energy content (power) may be measured (e.g. in W m−2). Radiation also behaves as a vibrating electrical and magnetic field moving in a particular direction, with the magnetic and electrical components vibrating perpendicular to one another and perpendicular to the direction of travel. The wave nature of radiation gives rise to the concepts of wavelength (λ, usually measured in nm), frequency (ν, measured in s−1, but often recorded in hertz, Hz), speed (c, the speed of electromagnetic radiation, which is 3 × 108 m s−1 in a vacuum), and direction. In other words, radiation is a vector quantity, where:

⇒ Equation [26.1] c = λν

Sometimes, it is necessary to rearrange the equation such that:
⇒ Equation [26.2] ν =
The electromagnetic spectrum.
Fig. 26.1 The electromagnetic spectrum.

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