7
Working Principle
A spectrophotometer basically consists of five
parts: a light source to supply electromagnetic
energy, a monochromator to isolate the wave-
length of interest and a stray light filter to elimi-
nate the unwanted second order radiation, a
sample compartment to accommodate the
sample solution, a detector to receive the trans-
mitted light and convert it to electrical signal, and
either a digital or analog display to indicate absor-
bance and transmittance. The block diagram to
the left illustrates the relationship among these
parts.
In your spectrophotometer, a light beam from the
lamp is focused on the entrance slit of the mono-
chromator and passes into the monochromator,
where the collimating mirror directs the beam to
the grating. The grating disperses the light beam
to produce the spectrum, a portion of which is
focused onto the exit slit of the monochromator
by the collimating mirror. From here the beam is
passed through a stray light filter which helps
eliminate unwanted second order radiation. The
beam then enters the sample compartment
where it is passed through the sample. The
sample may absorb a portion of the light beam.
Upon leaving the sample compartment, the beam
then falls on the silicon diode detector. The
intensity of the light beam causes the detector to
produce an electrical signal. This electrical signal
is then converted to transmittance or absorbance
and displayed.
I
NTRODUCTION
Light
Source
Mono
chomator
Sample
Compartment
Detector
Display
