COLORIMETER – PRINCIPLE, COMPONENTS, WORKING
& APPLICATIONS
PRINCIPLE OF COLORIMETER:
⇒ Colorimeter
is based on the photometric technique which states that When a beam of incident
light of intensity I0 passes through a solution, a part of the
incident light is reflected (Ir), a part is absorbed (Ia)
and rest of the light is transmitted (It)
The mathematical relationship between the amount of light absorbed
and the concentration of the substance can be shown by the two fundamental laws
of photometry on which the colorimeter is based.
Beer’s Law
⇒ This law states that the amount of light absorbed is directly
proportional to the concentration of the solute in the solution.
Lambert’s Law
⇒ The Lambert’s law states that the amount of light absorbed is
directly proportional to the length and thickness of the solution under
analysis.
PARTS OF COLORIMETER:
There are 5 essential parts in a calorimeter.
⇒ Light Source – The most common source of light
used in colorimeter is a tungsten filament.
⇒ Monochromator – To select the particular
wavelength filter or monochromators are used to split the light from light
source.
⇒ Sample holder – Test tube or Cuvettes are
used to hold the color solutions they are made up of Glass at the visible
wavelength.
⇒ Photo Detector System – when light falls on the
detector system, an electric current is generated, this reflects the
Galvanometer reading.
⇒ Measuring device – The current from the
detector is fed to the measuring device, the Galvanometer, shows
the meter reading that is directly proportional to the intensity of light.
WORKING OF THE COLORIMETER:
⇒ When using a colorimeter, it requires being calibrated first which
is done by using the standard solutions of the known concentration of the
solute that has to be determined in the test solution.
⇒There is a ray of light with a certain wavelength
that is specific for the assay is directed towards the solution. Before
reaching the solution the ray of light passes through a series of different
filters and lenses.
These lenses are used for navigation of the
colored light in the colorimeter and the filter splits the beam of light into
different wavelength and allows the required wavelength to pass through it and
reaches the cuvette containing the standard or Test solutions.
It analyzes the reflected light and compares with
a predetermined standard solution.
⇒ The galvanometer measures the electrical signals and displays it
in the digital form. That digital representation of the electrical signals is
the absorbance or optical density of the solution analyzed.
⇒ If the absorption of the solution is higher than there will be
more light absorbed by the solution and if the absorption of the solution is
low then more lights will be transmitted through the solution which affects the
galvanometer reading and corresponds to the concentration of the solute in the
solution.
APPLICATIONS OF THE COLORIMETER:
⇒ The colorimeter is commonly used for the determination of the
concentration of a colored compound by measuring the optical density or its
absorbance.
⇒ It can also be used for the determination of the course of the
reaction by measuring the rate of formation and disappearance of the light
absorbing compound in the range of the visible spectrum of light.
⇒ By colorimeter, a
compound can be identified by determining the absorption spectrum in the
visible region of the light spectrum.
