What is Colorimeter?

A Colorimeter is a light and sensitive device used to measure the transmittance and absorbance of light that passes through a liquid sample. The colorimeter device also measures the intensity or color concentration that develops upon introducing a particular reagent into a solution.

These are Divided into Two Types.

Color densitometers, which measures the density of primary colors,

Color photometers, which measures transmission and color reflection.

Usually, the Colorimeter is used to measure the known solute concentration in a given solution with the help of Beer-Lambert law. The Colorimeter was invented by Louis J Duboscq, in the year 1870.

Principle of Colorimeter

Let us discuss the principle of colorimeter. A photometric is a technique which states that when a beam of incident light of intensity Io passed through a solution, it occurs the following.

  • A part is reflected which is denoted as Ir

  • A part is absorbed which is denoted as Ia

  • The remaining light is transmitted, which is denoted as It

Thus, Io = Ia + Ir + It

To determine Ia, the measurement of It and Io is sufficient. Therefore, Ir is eliminated and the amount of light reflected is kept as constant to measure It and lo.

The Colorimeter is based on two fundamental photometry laws. Let us discuss them briefly.

  • Beer's law

This law states that the amount of light absorbed is always proportional to the solute concentration present in the solution.

Log10 Io/It = asc

Where c is the concentration of the solution, and as is absorbency index.

  • Lambert's law

A = log10 Io/It = asb

Where, as is the standard absorbance and A is the test absorbance of the test, and b is the thickness/length of the solution.

Diagrammatic Representation of a Colorimeter

(Image to be added soon)

Working of Colorimeter

As discussed in the Colorimeter's different principles, let us look at the working of colorimeter.

Step 1

Before going to start the experiment, it is essential to calibrate the Colorimeter. It can be done with the help of the standard solutions of the known solute concentration that has to be determined. Then, fill the standard solutions in the cuvettes and place it in the cuvette holder of the Colorimeter.

Step 2

A light ray of a particular wavelength specific for the sample is in the direction of the solution. The light travels through a series of various filters and lenses. The colored light, then navigates by taking the help of lenses, and the filter allows the split of a beam of light into different wavelengths allowing only the required wavelength to pass through and reach the standard test cuvette.

Step 3

As the light beam reaches the cuvette, it is transmitted, reflected, and absorbed by the solution. The transmitted ray falls on the photodetector system, where the intensity of transmitted light is measured. Now, the photodetector system converts the beam into the electrical signals and sends it to the galvanometer.

Step 4

The electrical signals that are measured by the galvanometer displays in the digital form.

Step 5

Formula to determine the substance concentration in the test solution is,

A = ∈cl

Where ∈ and l are constant for the standard and test solutions, 

AT = CT ---- (i)

AS = CS ---- (ii)

From the above two equations, we get the colorimeter formula as,

AT × CS = AS × CT

CT = (AT/AS) × CS

Where AT is the optical density/absorbance of the test solution, AS is the absorbance / optical density of the standard solution, CT is the concentration of the test solution, and CS is the standard concentration.

Colorimeter Uses

Let us look at some uses of colorimeter. We use a Colorimeter device to test the water quality by screening chemicals such as chlorine, cyanide, fluoride, dissolved oxygen, iron, zinc, hydrazine, and molybdenum. It is used in hospitals and medical laboratories to estimate biochemical samples, including plasma, urine, cerebrospinal fluid, serum, and a few more.        

Besides, it helps in the identification of counterfeit and substandard drugs. Most of the food industries use this device. Paints and textile manufacturers use a colorimeter. This device often checks the strength and durability of the colours in paints and fabrics to ensure a similar quality.

Colorimeter Applications

Few of the applications of colorimeter are explained here. Colorimeters are widely used to monitor bacterial growth or yeast culture. They provide highly accurate and reliable results when used for the assessment of color in bird plumage. They are also used to monitor and measure the colour in various foods and beverages, including sugar and vegetable products. Certain colorimeters can even measure the colors used in fax machines, copy machines, and printers.

A colorimeter is used for the basic research in chemistry laboratories, in addition, colorimeters have numerous practical applications including testing water quality by screening chemicals such as fluoride, zinc, chlorine, cyanide, iron, dissolved oxygen, molybdenum, and hydrazine. Also, they are used to determine the plant nutrient concentrations such as nitrate, ammonia, and phosphorus in soil or the hemoglobin in the blood. Besides, Colorimetry is a process used in textile manufacturing, color printing, and paint manufacturing for precise quality inspection.

FAQ (Frequently Asked Questions)

1. Mention Some Advantages and Disadvantages of Colorimetry?

Advantages of Colorimetry

  • It is fast, economical, and has a simple operation of a spectrometer.

  • It is a quite fast and convenient method to that of the gravimetric or volumetric processes, and they are easily optimized for automation.

  • To handle the Colorimeter, it does not require an experienced person.

Disadvantages of Colorimetry

  • The primary bottleneck of this method is that colorless compounds cannot be analyzed.

  • It needs a huge amount of samples for analysis.

  • It has low sensitivity.

  • The same colors of interfering material can create errors in results.

2. List the Types of Colorimeter?

The types of Colorimeters are listed below.

  • The Handheld Colorimeter determines the colour of an object, like an actual checking shade of clothes.

  • The Chemical type of Colorimeter finds the presence of colourless chemicals in water by allowing them to develop a colour reaction. Then, they compare the results to a known data body about the reactions of various substances.

  • Coming to the Gran Colorimeter measures the specific colour of a gemstone, such as a ruby, diamond, and a few other valuable stones.