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Study Notes: Overview of Qualitative and Quantitative Analysis
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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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