Download (4Mb) - Etheses - Saurashtra University

Chapter VI UV-Vis Spectroscopic….
wavelength as the absorption from the carbonyl group in diethyl ketone [39-
40].
The instrument used in ultraviolet-visible spectroscopy is called a UV-
vis spectrophotometer. It measures the intensity of light passing through a
sample (I), and compares it to the intensity of light before it passes through
the sample (Io). The ratio I/Io is called the transmittance and usually express in
percentage (%).
The basic parts of a spectrophotometer are a light source, a holder for
the sample, a diffraction grating or monochromator to separate the different
wavelengths of light, and a detector. The radiation source is often a tungsten
filament (400-2500 nm), a deuterium arc lamp which is continuous over the
ultraviolet region (200-400 nm), and more recently light emitting diodes (LED)
and xenon arc lamps for the visible wavelengths. The detector is typically a
photodiode or a CCD. Photodiodes are used with monochromators, which
filter the light so that only light of a single wavelength reaches the detector.
Figure: 6.6 Schematic diagram of single-beam UV-Vis spectrophotometer.
A spectrophotometer can be either single beam or double beam. In a
single beam instrument, all of the light passes through the sample. Io must be
measured by removing the sample. This was the earliest design, but is still in
common use in both teaching and industrial labs. In a double-beam
instrument, the light is split into two beams before it reaches the sample. One
beam is used as the reference and other beam passes through the sample.
237