Colorimeter - Beer’s Law, Lambert’s Law, Principle, Parts, Applications, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:48 PM IST

Colorimetry is a scientific technique that employs the Beer–Lambert rule to determine the concentration of coloured substances in solutions. A colorimeter is a colorimetry tool.It refers to a device that aids in the absorption of a given wavelength of light by specific solutions. It measures absorbance and wavelength between 400 and 700 nm (nanometer), i.e. from the visible spectrum of light. Using the Beer-Lambert rule, the colorimeter is often used to determine the concentration of a known solute in a given solution. In the year 1870, Louis J Duboscq devised the colorimeter

This Story also Contains

Working principle of colorimeter
Beer’s Law
Lambert’s Law
Parts of Colorimeter
Working of Colorimeter
Applications of Colorimeter
Colorimeter v/s Spectrophotometer

Working principle of colorimeter

Let as discuss the working principle of the colorimeter.The photometric technique is used in a colorimeter asserts that when a beam of incident light of intensity (I₀) passes through a solution, a portion of it is reflected (I_r), absorbed (I_a), and the rest is transmitted (I_t)

I₀ =I_r +I_a+I_t

Because of the measurement of (I₀), (I_r) is deleted in colorimeters, and it is sufficient to determine the value of (I_a). This is accomplished by utilising cells with equal characteristics to keep the amount of light reflected (I_r) constant. After that, (I₀), and (I_t), are calculated.

Colorimeter is based on two basic laws of photometry, which show the mathematical relationship between amount of light absorbed and the concentration of the substance.

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Beer’s Law

The amount of light absorbed is proportional to the amount of solute in solution, as per Beer's law.

Log₁₀(I₀/I_t)=a_s c

Where a_s=Absorbency index

c =Concentration of the solution

Lambert’s Law

According to Lambert's law, the amount of light absorbed and thickness or length of the solution are directly proportional

A = Log₁₀(I₀/I_t)= a_sb

Where,

A = Absorbance of the solution

a_s= Absorbancy index

b = thickness of the solution

Parts of Colorimeter

A colorimeter has five key components.

Light Source

A tungsten filament is the most popular light source in colorimeters.

Monochromator

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Filters or monochromators are used to separate the light from the light source to select a specific wavelength.

Sample holder

Color solutions are held in test tubes or cuvettes, which are composed of glass at visible wavelengths.

Photodetector system

An electric current is generated when light falls on the detection system, which reflects the Galvanometer reading.

Measuring device

The current from the detector is routed into the Galvanometer, which displays a metre reading that is directly proportional to light intensity.

Colorimeter diagram

Working procedure of galvanometer

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Working of Colorimeter

There are five steps involved in the working of colorimeter

It is necessary to calibrate the colorimeter before beginning the experiment. It's done with the help of standard solutions containing the known solute concentration to be determined. Fill the cuvettes with standard solutions and set them in the colorimeter's cuvette holder.
A light ray of a specific wavelength for the assay is sent in the direction of the solution. The light is filtered through a succession of lenses and filters. Colored light passes through lenses and the filter splits a beam of light into different wavelengths so that only the required wavelength can pass through the standard test solution in the cuvette.
The laser beam is transmitted, reflected, and absorbed by the solution when it reaches the cuvette. The photodetector device monitors the intensity of transmitted light when the transmitted ray hits it. It turns the data into electrical impulses, which it then sends to the galvanometer.
The galvanometer's electrical signals are shown in a digital format. The absorbance or optical density of the investigated solution is the digital representation of the electrical signals. If the solution absorbs more light, more light is absorbed by the solution, and if the solution absorbs less light, more light is transmitted through the solution, which determines the galvanometer reading
Formula for determining the concentration of a chemical in a test solution.

A = ∈cl

For standard and test solutions

∈ and l are constant

A_T= C_T

A_S= C_S

From these equations,

A_T× C_S= A_S× C_T

C_T= (A_T/A_S) × C_S

Where,

C_T= Concentration of the test solution

A_T= Absorbance/optical density of test solution

C_S= Standard concentration

A_S= Absorbance / optical density of standard solution

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Applications of Colorimeter

The colorimeter is a device that measures the optical density or absorbance of a coloured chemical to determine its concentration
A substance can be identified using a colorimeter by analyzing its absorption spectra in the visible area of the light spectrum.
It can also be used to determine the reaction's course by observing the rate of creation and disappearance of the light-absorbing compound in the visible spectrum of light.
It is utilized to calculate biochemical samples including urine, cerebrospinal fluid, plasma, and serum in laboratories and hospitals.
It is utilized in the production of paint.
It can be found in the textile and food industries.
It is used to analyze proteins, glucose, and other biological components quantitatively.
It is used to determine the quality of water.
It is used to figure out how much haemoglobin is in your blood.

The main advantage of colorimeter is that it is a low-cost method that is commonly employed in the quantitative examination of coloured samples, as well as one that is simple to carry and transport. The disadvantage is that it is not feasible to analyze colourless chemicals, and it does not work in the IR or UV regions.

Colorimeter v/s Spectrophotometer

The spectrophotometer consists of moving parts, is heavier, and is only suitable for laboratory use. The colorimeter consists of fixed parts and is lighter and therefore suitable for use in the field.
The spectrophotometer measures the amount of light that passes through a sample. Colorimeter measures light absorption.
The wavelength selector of the spectrophotometer is monochromator, wavelength range. The wavelength selector on the colorimeter is a color filter with a fixed wavelength.

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Frequently Asked Questions (FAQs)

1. What is the colorimeter's principle?

The method of determining the concentration of a coloured chemical in a solution is known as colorimetry. A colorimeter, also known by the name philtre photometer. It is an analytical equipment that is needed to calculate the concentration of a solution by measuring the absorption of a specific wavelength of light.. The colorimeter's working principle is based on Beer-law, and Lambert's which states that the amount of light absorbed by a colour solution is directly proportional to the concentration of the solution and the thickness of the solution

2. What makes a colorimeter different from a spectrophotometer ?

Ans: Let's discuss the difference between colorimeter and spectrophotometer. A colorimeter is a device that characterises colour samples in order to acquire objective colour characteristics measurements. A spectrophotometer is a sort of photometer (a light-measurement equipment) that can determine the intensity or, more precisely, the wavelength of light as a function of colour.

3. A colorimeter uses what wavelength?

Ans: A solution's colour might be intrinsic or produced by adding another chemical to it. The colorimeter measures the amount of light that is reflected through a sample at a wavelength that the user specifies. The front panel arrow keys can be used to select one of four wavelengths: 430 nm, 470 nm, 565 nm, or 635 nm.

4. What is meant by a photoelectric colorimeter?

Ans: A photoelectric colorimeter is a device that is used to quantify various chemicals such as glucose, blood urea, and blood enzymes.

5. What are the uses of a colorimeter?

Ans: A colorimeter is a device that determines the concentration of a coloured substance by detecting its optical density or absorbance. A colorimeter can be used to identify a chemical by studying its absorption spectra in the visible light spectrum. It can also be used to determine the reaction's progress by looking at the pace at which the light-absorbing molecule appears and disappears in the visible spectrum of light.

6. What is the role of complexing agents in colorimetric analysis?

Complexing agents react with the analyte to form colored complexes, allowing for the colorimetric determination of substances that are not naturally colored. They are crucial for expanding the range of analytes that can be measured using colorimetry.

7. How can you determine if a colorimetric method is suitable for a particular analyte?

To determine suitability, consider factors like the analyte's ability to form a colored complex, the stability of the color, the sensitivity of the method, potential interferences, and whether the absorbance falls within the linear range of the instrument.

8. How does the presence of suspended particles affect colorimetric measurements?

Suspended particles can scatter light, leading to erroneously high absorbance readings. This effect, known as turbidity, can be minimized by filtering the sample or using longer wavelengths where scattering is less pronounced.

9. What is Beer's Law and how is it applied in colorimetry?

Beer's Law states that the absorbance of a solution is directly proportional to its concentration when the path length is constant. In colorimetry, this law is used to determine the concentration of unknown solutions by comparing their absorbance to known standards.

10. How does the path length of the cuvette affect absorbance measurements?

According to Lambert's Law, absorbance is directly proportional to path length. Increasing the path length (using a longer cuvette) increases the absorbance, which can improve sensitivity for dilute solutions.

11. What is the difference between absorbance and transmittance?

Absorbance is the amount of light absorbed by a sample, while transmittance is the amount of light that passes through the sample. They are inversely related: as absorbance increases, transmittance decreases.

12. How does a monochromator differ from a filter in a colorimeter?

A monochromator selects a narrow band of wavelengths from a continuous spectrum, while a filter allows only specific wavelengths to pass through. Monochromators offer more flexibility in wavelength selection but are typically more expensive than filters.

13. How does the choice of wavelength affect colorimetric measurements?

The choice of wavelength is crucial in colorimetry as it should correspond to the maximum absorption of the analyte. Using the wrong wavelength can lead to reduced sensitivity and inaccurate results.

14. How does temperature affect colorimetric measurements?

Temperature can affect colorimetric measurements by changing the chemical equilibrium of the colored complex, altering the refractive index of the solution, or affecting the electronic transitions responsible for color. It's important to maintain consistent temperature during measurements.

15. What is the linear range in colorimetry and why is it important?

The linear range is the concentration range where the relationship between absorbance and concentration remains linear. It's important because measurements outside this range may not accurately reflect the true concentration of the analyte.

16. What are the main components of a colorimeter?

The main components of a colorimeter include a light source, monochromator or filter, sample holder (cuvette), photodetector, and a display or readout system. Each part plays a crucial role in measuring the absorbance or transmittance of light through a sample.

17. How does the principle of complementary colors apply to colorimetry?

The principle of complementary colors states that a solution absorbs light of a color complementary to its apparent color. For example, a blue solution primarily absorbs orange light. This principle helps in selecting appropriate filters or wavelengths for analysis.

18. How does colorimetry apply to environmental water analysis?

Colorimetry is widely used in water analysis to measure parameters like nitrate, phosphate, and heavy metal concentrations. It provides a simple, cost-effective method for monitoring water quality and detecting pollutants.

19. What are the limitations of colorimetry?

Limitations include interference from other colored substances, limited sensitivity compared to some other techniques, the need for visible light absorption, and potential inaccuracies at very high or low concentrations.

20. How does colorimetry contribute to quality control in industries?

Colorimetry is used in quality control to ensure product consistency, monitor production processes, and verify the concentration of active ingredients. It's particularly important in industries like food and beverage, pharmaceuticals, and chemical manufacturing.

21. What is a colorimeter and how does it work?

A colorimeter is an instrument that measures the intensity of color in a solution by analyzing how much light is absorbed or transmitted. It works based on the principle that the amount of light absorbed is proportional to the concentration of the colored substance in the solution.

22. Why is it important to use a blank or reference solution in colorimetry?

A blank or reference solution is used to calibrate the instrument and account for any absorbance not due to the analyte. This helps eliminate background interference and ensures accurate measurements of the sample's absorbance.

23. How can you improve the sensitivity of a colorimetric method?

Sensitivity can be improved by using a longer path length cuvette, concentrating the sample, choosing a more sensitive complexing agent, or selecting a wavelength that maximizes absorbance while minimizing interference.

24. What are some common sources of error in colorimetry?

Common sources of error include improper calibration, dirty cuvettes, bubbles in the solution, stray light, instrument drift, and chemical interferences. Careful technique and regular instrument maintenance can minimize these errors.

25. What is the difference between a single-beam and a double-beam colorimeter?

A single-beam colorimeter measures the sample and blank separately, while a double-beam colorimeter measures them simultaneously using two light paths. Double-beam instruments can compensate for fluctuations in light intensity and are generally more accurate.

26. What is the significance of the absorption spectrum in colorimetry?

The absorption spectrum shows how a substance absorbs light across different wavelengths. It's used to determine the optimal wavelength for analysis, which is typically the wavelength of maximum absorption for the analyte.

27. What is the Beer-Lambert Law?

The Beer-Lambert Law combines Beer's and Lambert's Laws, stating that absorbance is directly proportional to both concentration and path length. It's expressed as A = εbc, where A is absorbance, ε is the molar absorptivity, b is the path length, and c is the concentration.

28. What is the difference between qualitative and quantitative analysis in colorimetry?

Qualitative analysis uses color changes to identify the presence of specific substances, while quantitative analysis measures the intensity of color to determine the concentration of a substance. Colorimetry is primarily used for quantitative analysis.

29. What is the purpose of a calibration curve in colorimetry?

A calibration curve relates the measured absorbance to known concentrations of the analyte. It's used to determine the concentration of unknown samples by interpolating their absorbance values on the curve.

30. How does the pH of a solution affect colorimetric measurements?

pH can significantly affect colorimetric measurements by altering the chemical form of the analyte or the complexing agent, which can change the color intensity or shift the absorption spectrum. Maintaining consistent pH is often crucial for accurate results.

31. How does Lambert's Law differ from Beer's Law?

Lambert's Law focuses on the relationship between absorbance and path length, stating that absorbance is directly proportional to the path length when concentration is constant. Beer's Law relates absorbance to concentration at a fixed path length.

32. What is the significance of the molar absorptivity (ε) in the Beer-Lambert Law?

Molar absorptivity (ε) is a measure of how strongly a substance absorbs light at a given wavelength. It's a constant specific to each substance and is used in the Beer-Lambert Law to relate absorbance to concentration.

33. What is the significance of the extinction coefficient in colorimetry?

The extinction coefficient, also known as molar absorptivity, is a measure of how strongly a substance absorbs light at a given wavelength. It's used in the Beer-Lambert Law and is crucial for relating absorbance to concentration.

34. How does colorimetry compare to other spectroscopic techniques like UV-Vis spectroscopy?

Colorimetry is simpler and often less expensive than UV-Vis spectroscopy but is limited to visible wavelengths. UV-Vis spectroscopy can measure in both ultraviolet and visible regions, offering broader applicability and often higher sensitivity.

35. What is the role of Beer's Law in creating calibration curves?

Beer's Law provides the theoretical basis for the linear relationship between absorbance and concentration, which is used to construct calibration curves. Deviations from linearity can indicate limitations in the method or instrument.

36. What is the difference between a colorimeter and a spectrophotometer?

While both measure light absorption, a colorimeter typically uses filters to select specific wavelengths and is limited to the visible spectrum. A spectrophotometer can measure across a wider range of wavelengths, including UV and near-infrared, and often offers higher resolution and sensitivity.

37. How does the concentration of a solution affect its color intensity?

According to Beer's Law, the color intensity (absorbance) of a solution is directly proportional to its concentration. As concentration increases, the solution appears more intensely colored, and more light is absorbed.

38. What is the importance of using matched cuvettes in colorimetry?

Matched cuvettes ensure consistent path length and optical properties, reducing errors that could arise from variations between sample holders. This is particularly important when comparing samples or using a single-beam instrument.

39. How can matrix effects impact colorimetric measurements?

Matrix effects occur when components of the sample other than the analyte interfere with the measurement. These can cause errors by absorbing light, altering the chemical equilibrium, or changing the refractive index of the solution.

40. What is the role of indicator dyes in colorimetric analysis?

Indicator dyes change color in response to specific chemical conditions, such as pH or the presence of certain ions. They are used to create visible color changes that can be measured colorimetrically, expanding the range of analytes that can be detected.

41. How does colorimetry apply to biochemical analysis?

In biochemistry, colorimetry is used to quantify proteins, enzymes, and metabolites. Common applications include the Bradford assay for protein quantification and enzyme-linked immunosorbent assays (ELISA) for detecting specific biomolecules.

42. How does light scattering affect colorimetric measurements?

Light scattering, caused by particles in the solution, can lead to erroneously high absorbance readings. This effect is more pronounced at shorter wavelengths and can be minimized by filtering samples or using longer wavelengths.

43. What is the role of colorimetry in forensic science?

In forensics, colorimetry is used for various analyses, including drug testing, blood alcohol determination, and trace metal detection. It provides rapid, on-site testing capabilities that can be crucial in criminal investigations.

44. How does the bandwidth of the light source affect colorimetric measurements?

The bandwidth of the light source can impact the specificity and sensitivity of the measurement. Narrower bandwidths generally provide better selectivity but may reduce the overall light intensity, potentially affecting the signal-to-noise ratio.

45. What are some strategies for dealing with samples that are too concentrated for direct measurement?

Strategies include diluting the sample, using a shorter path length cuvette, or selecting a less sensitive wavelength. The choice depends on the specific situation and the desired accuracy of the measurement.

46. How does colorimetry contribute to the analysis of food additives and colorants?

Colorimetry is used to quantify food dyes and additives, ensuring compliance with regulations and quality standards. It can determine the concentration of natural and artificial colorants in food products.

47. What is the importance of maintaining linearity in colorimetric measurements?

Linearity ensures that the relationship between absorbance and concentration remains consistent, allowing accurate quantification across a range of concentrations. Deviations from linearity can lead to errors in concentration determinations.

48. How does the presence of multiple absorbing species affect colorimetric analysis?

When multiple species absorb at the same wavelength, their individual contributions to the total absorbance are additive. This can complicate analysis but can also be used advantageously in certain multi-component analyses.

49. What is the role of colorimetry in monitoring chemical reactions?

Colorimetry can be used to monitor the progress of reactions that involve color changes, such as acid-base titrations or redox reactions. It allows for real-time tracking of reaction kinetics and endpoint determination.

50. How does the choice of solvent affect colorimetric measurements?

Solvents can affect the absorption spectrum of the analyte, potentially shifting the wavelength of maximum absorption. They can also impact the chemical equilibrium of colored complexes and the overall sensitivity of the method.

51. What are some applications of colorimetry in clinical chemistry?

In clinical chemistry, colorimetry is used for various diagnostic tests, including measuring glucose levels, determining cholesterol concentrations, and assessing liver and kidney function through enzyme activity measurements.

52. How does colorimetry compare to visual color comparison methods?

Colorimetry provides more objective and quantitative results compared to visual color comparison. It eliminates subjectivity, offers greater sensitivity, and can detect subtle color differences that might be missed by the human eye.

53. What is the significance of the detection limit in colorimetric analysis?

The detection limit is the lowest concentration of analyte that can be reliably distinguished from a blank. It's important for determining the sensitivity of the method and its applicability to trace analysis.

54. How does colorimetry contribute to the field of art conservation?

In art conservation, colorimetry is used to analyze pigments, monitor color changes over time, and ensure accurate color matching during restoration. It provides a quantitative way to document and preserve the visual characteristics of artworks.

55. What are some emerging trends or technologies in colorimetric analysis?

Emerging trends include miniaturization for portable devices, integration with smartphone technology for field analysis, development of new chromogenic reagents for improved selectivity, and combination with other techniques like microfluidics for enhanced performance and automation.