Colorimeter

Scientific instruments are tools and devices that are used for scientific functions, scientific research, the study of nature, and theoretical research. A colorimeter is a scientific instrument that is used in colorimetry. 

Colorimetry is a scientific technique used to determine the concentration of coloured substances in solutions with the Beer-Lambert rule. It was first discovered by Louis J Duboscq, an instrument maker and photographer. A colorimeter is used to measure the concentration of solute in any solution. It is also a device that measures the density of a specific solution to absorb specific wavelengths of light.

Parts of a Colorimeter

A colorimeter is constructed of these parts:

• A filament bulb: Used as a light source.

• Adjustable aperture

• Coloured filters: Optical filters are present for different wavelengths to absorb by the solute.

• A cuvette: It is a glass tube to hold the solution.

• A detector: A photoresistor is used as a detector.

• Display metre: It is a display in the front of the instrument to show the results.

• Voltage regulator: To avoid fluctuation.

Principle of Colorimeter

It is based on a photometric technique. When an incident light beam of intensity Io passes through a solution, then the following things occur:

A part of the incident light is reflected I_r.

A part of the incident light is transmitted I_t.

A part of the incident light is absorbed, i.e., I_a.

Thus, I_o =I_r + I_t + I_a

I_r is removed because the measurement of I_o is sufficient to determine I_a. To calculate I_o and I_t, the amount of light that is reflected is kept constant.

Colorimeter works on two basic laws of photometry: Lambert’s law and Beer’s law.

Beer’s law: 

This law is given by a German mathematician, August Beer. This law says that there is a proportionality between the amount of light absorbed and the concentration of the solution.

Lambert’s Law:

This law was given by Pierre Bouguer. This law states that the amount of light that is absorbed is proportional to the thickness and length of the solution.

The expression for Beer-Lambert’s law is given as,

A = εbC 

Where ε is the molar absorptivity, b is the length of the light path, C is the concentration of the solution, and A is the absorbance.

Working of colorimeter

The first step in using a colorimeter is to calibrate it. It is completed by using a standard solution. The standard solution is to pour it into a cuvette and put it in a cuvette holder and a light is passed through the solution. 

The light is passed through many lenses and filters present in the colorimeter. When the light is passed through the cuvette, it will be either reflected, transmitted or absorbed by the sample. 

The transmitted light is measured by the detector and calculates the intensity of light, which it is sent to the galvanometer and displayed on the screen. Then, the formula is used to calculate the concentration of the solution.

Uses of colorimeter

• A colorimeter is used in paint industries for the production of paints.

• It is used in food industries to measure the colours of fruits, vegetables, dairy products, oils, spices, cereals and beverages.

• It is used in determining the quality of water.

• In biochemical sectors, it helps calculate the samples like urine, serum, and cerebrospinal fluids and measure the amount of haemoglobin in the blood.

• In the textile industry, it is used to measure the obtainable volume of wool. In dyeing and printing, a colorimeter is used to measure the whiteness of compounds.

Conclusion

A colorimeter is a light-sensitive instrument invented in the year 1870. It helps a solution to absorb light of a specific wavelength. Furthermore, it calculates the transmittance and absorbance of light passing through a liquid. 

Colorimeter works on the principle that coloured compounds absorb light of a specific wavelength. It is also used to determine the coloured compounds in a solution. The instrument helps in determining the concentration of liquids and coloured liquid for biological purposes, and is used in almost every industry. It is portable and easy to use. It shows the result on the screen present in the instrument.