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Wednesday, March 4, 2020

Principle and Procedure of Colorimeter

What is a Colorimeter?

A colorimeter is a light-sensitive tool used to measure the absorption and transmission of light that passes through a sample solution. A colorimetric device works based on Beer Lambert's law. The photoelectric colorimeter is a sensitive apparatus intended for use in various colorimetric analyses such as soil component analysis, building materials, water analysis, food ingredients, textile products, additives, and employ in different manufacturing processes.  

Colorimeter Principle:

Colorimetry is a sensitive tool used to determine the intensity and concentration of a sample at a particular wavelength. In general, two types of colorimeters are used which are spectrophotometers and tristimulus colorimeters. The colorimeter principle works based on Beer-Lambert's law. This rule states that the absorption of light when passing through a medium is directly proportional to the intermediate convergence. While using a colorimeter, there is a beam of light wherein a given wavelength is directed toward a liquid sample. By entering a sample solution, the light beam travels through a series of different lenses, and the microprocessor is used to determine the absorption or emission of light through the liquid sample. If the concentration of the sample is high, more light will be absorbed and if the sample has a low concentration, it will transmit more light.

You may determine colorimetric reactions on a colorimeter or a spectrophotometer. Both measure the intensity of light that passes through a liquid sample and convert the intensity of this light into a concentration based on a specific calibration curve.

The colorimetry follows the principles of the Beer-Lambert law is expressed as: 
A = Ɛ x b x c
A is the absorbance of the sample component
Ɛ is a wavelength-dependent absorptivity coefficient
b is the path length of the cell
c is the concentration of the analyte

Working principle of colorimeter:

The colorimeter's working principle depends on the Beer-Lambert law which states that the amount of light absorbed by a sample corresponds to the sample solution concentration and the length of a light path through the solution. A low voltage lamp that is turned on by a constant voltage renders the light source. This goes through a color filter and liquid sample on the detector. The current generated by the photocell is then converted into a voltage to display the result on the screen. The current that the photocell generates will then be converted to voltage to show the result of either an absorbance or a transmittance on the screen.

Types of Colorimeter:

The tristimulus colorimeter and spectrophotometer are the types of colorimeter used for color measurement.
Tristimulus colorimeter: Tristimulus colorimeter is usually used for quality control, and appropriate with color variations and resistance determination. The tristimulus method measures the light reflected from the object to have a similar sensitivity using three separate sensors.
Spectrophotometer: A spectrophotometer is a device that can determine light intensity as a function of color, or more precisely, the wavelength of light, and other liquid samples. This detects both the entire UV spectrum in the range of 200-400 nm and the visible range of 400-800 nm. It gives accurate data by providing the wavelength of the sample absorbance or transmittance properties by wavelength spectral analysis. A spectrophotometer is simple and fast to operate and is most commonly used for light absorption measurement.

Colorimeter Procedure:

Before beginning a colorimetry analysis, we must recognize the various parts essential to perform the process.
Light source: Generally a tungsten or xenon lamp is used to produce the light.
Filter: It is made of colored glass, and is used to choose the light of narrow wavelength.
Cuvette: It is used to hold the solution of the sample. The monochromatic light passes through the sample solution put in a cuvette. Cuvettes are made up of special quartz or glass.
Detector or Photocell: it is used to detect the light transmitted through the sample. It is the photosensitive component that transforms light energy into electric energy.

Experimental Procedure of Colorimeter:

  • A colorimeter requires the first calibration using standard solutions of the specified solute concentration to be measured in a test sample. 
  • Prepare samples according to the procedure. 
  • Turn the instrument ON and allow it to warm up for 10-15 minutes. 
  • Choose the correct filter. 
  • Select the appropriate mode, i.e. % transmittance or absorbance. 
  • Insert the test tube containing the “Blank” or “Reference” solution. 
  • Make auto-zero with the blank solution. 
  • Remove the test tube containing the blank solution and insert the sample solution. 
  • Note down the reading in %T mode or optical density.

Colorimeter Applications:

  • It uses to confirm the quality and consistency of fabric and paint colors 
  • Applications of colorimeter have the qualitative and quantitative analysis of the samples. 
  • The food industry uses this to ensure the quality of the product. 
  • It is used to determine the quality of the food, to ensure that it does not spoil by determining its particular color. 
  • It can also be used to calculate a reaction's path by evaluating the rate of formation and the disappearance of light-absorbing analytes within the range of the visible light spectrum. 
  • The quality of the water is measured using colorimetry. 
  • It is used by manufacturers of paints, pharmaceuticals, and textiles. 
  • Colorimetry is frequently used to determine the concentration of the sample by determining the transmittance, optical density, or absorption thereof. 
  • By determining the absorption spectrum in the visible range, the component can be identified. 

The Advantages of Colorimeter are as Follows.

  • It is cost-effective, rapid, and is easy to operate. 
  • Compared to the volumetric or gravimetric processes it is a fast and convenient technique. 
  • No expert is required to handle this. 
  • Using the colorimetry process the chemical substances can be identified in the water. 
  • It subjected colored compounds to quantitative analysis. 
  • It can be used in the quantitative analysis of colored compounds. 
  • Another advantage of colorimeter is that it's a portable system that convenient to carry  

The Disadvantages of Colorimeter are as Follows.

  • Not analyzing colorless compounds is the major disadvantage of colorimetry. 
  • It requires more sample amounts for analysis. 
  • It requires the standard solution to be prepared. 
  • It has a lower sensitivity than other techniques. 
  • Colorimetry is not functioning in UV and IR regions. 
  • The accurate bandwidth of wavelengths can be essential for a more precise analysis of the molecules.

Commonly asked questions on colorimeter are as follows.

What is a Colorimeter?
A colorimeter is a light-sensitive tool used to determine the emission and absorption of light that passes through a sample solution.

What are the types of colorimeters?
In colorimetry, two types of analysis are used: the spectrophotometer and the tristimulus colorimeter.

Which light source is used in the colorimeter?
Generally, a tungsten or xenon lamp is used as a light source in colorimetry.

What is the major advantage of colorimeter?
The major advantage of colorimeter such as economical, quick, and has simple operation.

What is the major difference between spectrophotometer and colorimeter?
The major difference between a spectrophotometer and a colorimeter is that the spectrophotometer determines the absorption, or transmittance as a function of wavelength, and can operate on a range of wavelengths, i.e. UV or VIS, while a colorimeter is a tool that determines the absorption of particular colors at a fixed wavelength.

What is the major difference between absorbance and transmittance?
The major difference between absorbance and transmittance is that absorbance is to determine the amount of light absorbed by the analyte when a beam of light travels through it. Whereas, transmittance is the amount of light transmits by the analyte when a beam of light travels through it.


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