Ultraviolet Visible Spectroscopy UV/Vis

Ultraviolet - Visible Spectroscopy (UV/Vis): 

Principle :  It involves the absorption of electromagnetic radiation by the substances in the

ultraviolet and visible regions of the spectrum. This will result in changes in the electronic

structure of ions and molecules through the excitations of bonded and non-bonded electrons.

Instrumentation :  It consists of a dual light source viz., tungsten lamp for visible range and

deuterium lamp for ultraviolet region, grating monochromator, photo-detector, mirrors and

glass or quartz cells.

NOTE:  For measurements to be made under visible region both glass and quartz cells can be 

used. For the measurements under ultraviolet region, only quartz cell should be used, since, 

glass cells absorb ultraviolet rays.

There are two types of instrumental designs for this technique as single beam and double

beam spectrophotometers. However double beam spectrophotometers are widely used and

following is the outline of the instrument:

Applications :   It is the most widely used technique  for quantitative molecular analysis, for

this Beer-Lambert law is applied. Sometimes it is used in conjunction with other techniques

such as NMR, IR, etc., in the identification and structural analysis of organic compounds. For

qualitative analysis it provides valuable information through the absorption spectrum which

is unique for a given compound.

Disadvantages :  Samples should be in solution. Mixture of substances poses difficult to

analyse and requires prior separation. Interference from the sample’s matrix makes the

measurement difficult.