Spectroscopy is an extension of microscopy which in itself encompasses the microscopy that was previous discussed. In short, spectroscopy is the use of electromagnetic energy to study matter and to interpret results. Microscopy can be viewed as spectroscopy of the visible portions of light where as spectroscopy is said to encompass the entirety of the electromagnetic spectrum. Spectroscopy is useful since only a very small quantity of sample is needed for analysis. In addition, samples may be reused after analysis with IR, NMR or UV spectroscopy.

Absorbance Spectroscopy – UV/VIS spectrophotometry

One of the simplest types of spectroscopy is UV/VIS spectrophotometry. This paper has already mentioned how color can be used to analyze an unknown for preliminary tests. UV/VIS Spectrophotometry takes this principle and applies the principles of electromagnetic absorption of energy to it. Chemical structures can absorb energy and reflect energy. In most cases related to forensic pharmacology, color is due to the absorption of light by conjugated pi systems of two nearby elements of a molecule (in other substances such as metals, color is due to unique absorption that is characteristic of that the element(s) present).

A spectrophotometer takes the absorption information of a substance diluted into a liquid sample in order to obtain an output of absorption using Beers’ Law.

In Spectrophotometry Cell length is controlled for. The Coefficient and Concentration for unknowns is not usually known in forensic analysis, therefore this method is not utilized often for dealing with unknowns.

Although this method is more precise than the visual analysis of color, it is used far less in presumptive tests. The reasons for this are primarily due to the similarities in many UV/VIS spectra and the need to have a pure analyte for analysis.