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14 May 2021

Colorimeter | Principle | Part | Advantages and disadvantages | Applications

 What is a colorimeter?

A colorimeter is a piece of equipment used in colorimetry. It refers to a system that aids in the absorption of a certain wavelength of light by a specific solution. Using the beer lambert law, the colorimeter is used to determine the concentration of a specified solute in a given solution.

Principle of colorimeter:

It is a photometric technique which states that when a beam of an incident of the intensity I০ passes through a solution, the following occur:

  • A part of it is reflected which is denoted as Ir
  • A part of it is absorbed which is denoted as Ia
  • The rest of the light is transmitted and is denoted as It
Therefore Io = Ir + Ia + It

Where 

Ia  = the measurement of  Io and It is sufficient therefore Ir is eliminated. To calculate Io and It, the amount of light reflected is kept constant.

A colorimeter is based on two basic photometric rules

Beer's law:

The amount of light absorbed is proportional to the solute concentration in the solution, according to this law.

LOg10 Io/It = As * C

Where, 

As is absorbency index

C is the concentration of the solution

Lambert law:

The amount of light absorbed is proportional to the length and thickness of the solution used for analysis, according to this law.

A = log10 Io/It = As * B

Where 

A is the test absorbance of the test

As is the standard absorbance

B is the length/thickness of the solution

Part of colorimeter:

There is 5 essential part of colorimeter:

  1. Light source
  2. Monochromator
  3. Sample holder
  4. Photodetector system
  5. Measuring device
Light source: The most common source of light used in the colorimeter is a tungsten filament.

Monochromator: To pick a specific wavelength, monochromators or filters are used to split the light from the source.

Sample holder: Color solutions are kept in test tubes, which are made of glass with a visible wavelength.

Photodetector system: As light strikes the photodetector device, an electric current is produced, which is used to produce the reflected galvanometer reading.

Measuring device: The current from the detector is fed to the galvanometer, which displays a meter reading that is directly proportional to the light intensity.

Working of colorimeter:


Working of colorimeter

  • It is important to calibrate the colorimeter before beginning the experiment. It's done with the help of standard solutions containing the calculated solute concentration. Place the cuvettes in the colorimeter's cuvette holder and fill them with normal solutions.
  • In the direction of the solution is a light ray of a certain wavelength that is specific for the assay. The light is filtered through a series of lenses and filters. The colored light is guided by lenses, and the filter splits a beam of light into different wavelengths, allowing only the appropriate wavelength to pass through and enter the regular test cuvette.
  • When the light beam crosses the cuvette The solutions transmit, reflect, and absorb the light. The photodetector device tests the strength of transmitted light when the transmitter ray hits it. It transforms it into an electrical signal, which it then sends to the galvanometer.
  • The electrical signal measured by the galvanometer is displayed in digital form.
  • Formula to determine substance concentration in test solutions
                A = 𝞊cl
for standard and test solutions:

𝞊 and i are constant

AT = CT...................(1)
AS = CS...................(2)

AT * CS  = AS * CT

CT  = (AT / AS) * CS

Where,

CT = Test solution concentration

AT  = Absorbance density of test solution

CS = the standard concentration

AS = Absorbance/optical density of standard solution

Advantages and disadvantages of colorimeter:

Advantages:

  • Result available in less than 1 second
  • A handheld and pocket-sized colorimeter can make between 100 and 300 measurements of four AA batteries.
Disadvantages:
  • The colorimeter is fairly expensive.
  • Some surfaces reflect light, making it difficult to take measurements.

Uses of colorimeter | Applications of colorimeter
  • It's used in the production of paint.
  • It's used in the textile and food industries, among other things.
  • It's used to figure out how much hemoglobin is in your blood.
  • It is used to analyze proteins, glucose, and other biochemical compounds quantitatively.
  • In laboratories and hospitals, it's used to calculate biochemical samples like urine, cerebrospinal fluid, plasma, and serum.
  • It's used to figure out how thick water is.
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