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Study Notes: Overview of Qualitative and Quantitative Analysis

UV-Vis spectroscopy is applied for both qualitative and quantitative analysis. The former concerns identification of an unknown substance and is frequently achieved through comparison of the spectrum of a solution of the unknown with a reference spectrum (remember that a peak(s) represents a chromophore and therefore a particular structural element).

The amount of qualitative information available is, however, rather limited because the spectra generally show only a few broad absorption bands. Quite often UV-Vis spectroscopy is used in combination with other qualitative techniques to build up a picture that enables the absolute identification of an unknown.

By far the greatest application of UV-Vis spectroscopy relates to quantitative analysis. Beer’s Law, which describes the simple linear relationship between absorbance and concentration, is the basis of a multitude of quantitative analytical methods using this technique (to study or refresh yourself on this topic refer to Spectroscopic Concepts and Principles).

Quantitative UV-Vis spectroscopy is characterised by:

  • wide application to organic and inorganic compounds
  • analysis of very dilute solutions (< 10-2 M)
  • good sensitivities typically of the order of 10-4 to 10-5 M
  • moderate to high selectivity (aided by sample preparation procedures)
  • good accuracy
  • ease and convenience of measurement and data acquisition.

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