What is Colorimetry?
Colorimetry is the science of measuring colour using an objective numerical device rather than subjective responses. It has a significant impact on colour generation, rendition, and interpretation in all areas. The essence of the light, the optical properties of the object itself, and the human eye's reaction all influence how we perceive the colour of an object. Colorimetry quantifies these characteristics and incorporates the concepts of standard illumination and observers, resulting in colour representations like RGB, XYZ, L*a*b*, and L*C*h that clearly describes the colour.
What is the Colorimetry Machine Working Principle?
Let us first discuss the colorimeter definition, The colorimeter is a device that is based on Beer-law, Lambert's which states that the absorption of light transmitted through a medium is proportional to the concentration of the medium.
A beam of light with a particular wavelength is passed through a solution by a series of lenses, which guide the coloured light to the measuring device in a colorimeter.
According to the colorimetric method definition, it compares the colour to a pre-existing norm. The absorbance or percentage transmittance is then calculated by a microprocessor. More light would be absorbed if the solution's concentration is higher, which can be determined by comparing the amount of light at its source to that after passing through the solution.
Several sample solutions of known concentration are first prepared and analysed to assess the concentration of an unknown sample. After that, the concentrations are plotted against absorbance on a line, yielding a calibration curve. To calculate the concentration, the results of the unknown sample are compared to those of the known sample on the curve.
What is Beer-Lambert Law?
The Beer-Lambert Law (also known as Beer's Law) describes the relationship between light attenuation and the properties of a material. The concepts of light transmittance and absorbance by material are first presented in this article, accompanied by an explanation of the Beer-Lambert Law.
Before, starting with the Beer-Lambert law, let us first understand the meaning of absorbance and transmittance.
Consider monochromatic light, which has an incident intensity of I0 and a transmitted intensity of I, which is transmitted via a solution.
The solution's transmittance, T, is defined as the ratio of transmitted intensity, I, to incident intensity, I0, and can range from 0 to 1.
T = I/IO
However, it is more generally expressed as a transmittance percentage:
T% = 100 I/IO
The following relationships link the solution's absorbance, A, to the transmittance and incident and transmitted intensities:
A = Log10 IO/I
A = -Log10T
The transmittance and absorbance have a logarithmic relationship, with an absorbance of 0 corresponding to 100% transmittance and an absorbance of 1 corresponding to 10% transmittance. A 510 nm laser is passed through three solutions of Rhodamine 6G with different absorbances to demonstrate the effect of the absorbance of a solution on the attenuation light passing through it.
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Since absorbance is a dimensionless quantity, it should be treated as such. However, it is very common to see units of AU mentioned after the absorbance, which are said to represent arbitrary units of absorbance. These units are unnecessary and should be avoided at all costs. Another common occurrence is when the term optical density, or OD, is used instead of absorbance. Optical density is an older concept that is synonymous with absorbance in colorimetric spectroscopy; however, the IUPAC discourages the use of optical density in place of absorbance.
The Beer-Lambert law states that the absorbance of a solution is proportional to its concentration, molar absorption coefficient, and optical coefficient:
A = ECL
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The molar absorption coefficient is a sample-dependent property that indicates how strong an absorber a sample is at a given wavelength. The length of the cuvette used for the absorbance calculation is usually 1 cm, and the concentration is simply the moles L-1 (M) of the sample dissolved in the solution.
The Beer-Lambert law states that the concentration and absorbance of a solution have a linear relationship, allowing the concentration of a solution to be measured by calculating its absorbance. To illustrate this linear dependence, the Dual Beam Spectrophotometer should be used to test the absorption spectra of solutions in water, and a linear calibration curve of the absorbance versus concentration was produced from these absorption spectra. The concentration of an unknown solution can be measured using this calibration curve by calculating its absorbance, which is the main application of the Beer-Lambert Law.
Graph Between Absorbance and Wavelength
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Graph Between Absorbance and Concentration
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What is Colourimetry Design?
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A light source, a cuvette containing the sample solution, and a photocell for detecting the light passing through the solution are the three main components of colorimeter.
To generate colour, the instrument is also equipped with coloured filters or specific LEDs. An analogue or digital metre may display the output of a colorimeter in terms of transmittance or absorbance.
A voltage regulator can also be used in a colorimeter to protect it from variations in mains voltage. Some colorimeters are compact and can be used on-site, whereas others are larger, bench-top instruments that can be used in laboratories.
What is Colorimetry Machine Part?
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The Essential Parts of Colorimeter are:
A source of light (often an ordinary low-voltage filament lamp).
An aperture that can be changed.
Filters in various colours.
The working solution is held in a cuvette.
To calculate the transmitted light, a detector (usually a photoresistor) is used.
A metre that shows the detector's performance.
In addition, there may be:
A voltage regulator; a second light direction, cuvette, and detector; and a voltage regulator to protect the instrument from mains voltage fluctuations. This allows for better precision by comparing the working solution to a "blank" made up of pure solvent.
For education and science, there are several commercialised colorimeters as well as open-source models with construction documentation.
Colorimeter Modern Models for Colour and Appearance
Colorimetry systems such as the ones mentioned above can only determine the colour of an isolated sample when viewed against a neutral grey backdrop. Almost all colours, on the other hand, are seen against a variety of backgrounds, with varying fields of view, viewing conditions, and levels of adaptation to that environment. The sample's perceived colour can be influenced by the ambient colours or patterns in ways that the CIE L*a*b* system cannot anticipate. More complex models that account for these factors have been developed; the CIE recently recommended the CIECAM 97s model for further research. In these days of digital images and global communication, colour appearance models are becoming increasingly popular. An effective colour appearance model at the heart of the colour management system is needed for faithful reproduction of an image from computer screen to printed hard copy.
Colorimeter vs Spectrophotometer
Spectrophotometers, like colorimeters, are used to measure a substance's colour absorbing properties. The spectrophotometer calculates transmittance and reflectance as a function of wavelength, while the colorimeter measures the absorbance of individual colours.
Spectrophotometers measure the transmittance and reflectance of light in all colours and show how they change as the colour is changed. Colorimeters only work in the visible range of the electromagnetic spectrum, while spectrophotometers work in both visible and infrared radiation. Spectrophotometers can show accurate Beer's law results and can be used as colorimeters, but they are much more expensive and complex.
Colorimeter Uses
Colorimeters are commonly used to track bacterial or yeast culture growth.
When used to measure colour in bird plumage, they provide dependable and highly accurate results.
They're used to check and quantify the colour of a variety of foods and drinks, including sugar and vegetable products.
Colorimeters are devices that can calculate the colours used in copy machines, fax machines, and printers.
Colorimeters are used to monitor water quality by screening chemicals such as chlorine, fluoride, cyanide, dissolved oxygen, iron, molybdenum, zinc, and hydrazine, in addition to being used for basic research in chemistry laboratories.
They're also used to figure out how much ammonia, nitrate, and phosphorus are in the soil or how much haemoglobin is in the blood.
Colorimetry is also used for detailed quality inspection in colour printing, textile manufacturing, and paint manufacturing.
The pulp and paper industry has been one of the main drivers and beneficiaries of recent CIE colorimetry advancements. Despite the industry's need for correct colorimetry and compliance with the CIE's guidelines and findings, the more pressing economic concerns have been achieving reliable, repeatable, and reproducible measurements.
Colour can also be calculated, particularly in newspapers, where the colour is referred to as the paper's hue.
This system is used to check for chemicals including chlorine, fluoride, cyanide, dissolved oxygen, iron, molybdenum, zinc, and hydrazine in water. It may also be used to calculate the levels of plant nutrients in the soil (such as phosphorus, nitrate, and ammonia) or haemoglobin in the blood.
It also aids in the detection of substandard and counterfeit medications. His device is widely used in the food industry.
Colorimeters are used by paint and textile manufacturers. This system often inspects the quality and durability of paints and fabrics to ensure that they are of the same high standard.
Difference Between Colorimeter and Calorimeter
A calorimeter is a device that is used to measure the heat generated by chemical reactions or physical changes, as well as heat energy. Among the most popular types are differential scanning calorimetry, isothermal microcalorimetry, titration calorimetry, and accelerated rate calorimetry. A simple calorimeter is simply a thermometer connected to a metal container filled with water and suspended over a combustion chamber. It's one of the instruments used in thermodynamics, chemistry, and biochemistry study.
To calculate the enthalpy change per mole of a substance A in a reaction between two substances A and B, the substances are applied to a calorimeter separately, and the initial and final temperatures (before and after the reaction) are registered. The energy released or consumed during the reaction is calculated by multiplying the temperature change by the mass and basic heat capacities of the substances. The enthalpy change of a reaction is calculated by dividing the energy change by the number of moles of A current.
A colorimeter is a colorimetry system that tests the absorbance of specific wavelengths of light by a solution. The Beer-Lambert law, which states that the concentration of a solute is proportional to the absorbance, is widely used to calculate the concentration of a known solute in a given solution.
Types of Colorimeter
Handheld colorimeters are used to decide the colour of an item, such as determining the exact hue of clothing.
Chemical colorimeters detect the presence of colourless chemicals in water by inducing a colour reaction in them. They then link the findings to a database of information on the reactions of various substances.
The Gran Colorimeter is a device that determines the exact colour of a gemstone, such as a diamond, ruby, or other valuable stone.
Did You Know That?
In the specification, calculation, and regulation of optical properties in pulp and paper products, CIE Colorimetry is commonly used. Their grading is based on the optical properties of brightness, whiteness, opacity, and glossiness, which are critical in determining their commercial value.
Colorimetry is also used for detailed quality inspection in colour printing, textile manufacturing, and paint manufacturing.
FAQs on Colorimetry
1. What is colorimetry in the context of chemistry?
In chemistry, colorimetry is an analytical technique used to determine the concentration of a coloured compound in a solution. It works by measuring the amount of light of a specific wavelength that is absorbed by the solution. This method is based on the principle that the absorbance of light is directly proportional to the concentration of the coloured substance, allowing for quantitative analysis.
2. What is the fundamental principle behind colorimetry?
The fundamental principle of colorimetry is the Beer-Lambert law. This law states that the amount of light absorbed by a coloured solution is directly proportional to two factors: the concentration of the solute and the path length of the light through the solution. By measuring the light absorption, we can accurately calculate the substance's concentration.
3. What is the Beer-Lambert Law and its formula?
The Beer-Lambert Law is a crucial equation in colorimetry that relates light attenuation to the properties of a material. It provides a linear relationship between absorbance and concentration, making it possible to determine an unknown concentration.
The formula is expressed as:
A = εcl
Where:
- A is the Absorbance (dimensionless).
- ε (epsilon) is the molar absorption coefficient, a constant specific to the substance at a given wavelength (units: L mol⁻¹ cm⁻¹).
- c is the concentration of the substance in the solution (units: mol L⁻¹).
- l is the path length of the cuvette, which is the distance the light travels through the solution (usually 1 cm).
4. What are the main components of a colorimeter?
A standard colorimeter consists of several essential parts that work together to measure light absorbance. These components are:
- A light source, typically a low-voltage filament lamp.
- A set of coloured filters or LEDs to select a specific wavelength of light that the solute absorbs most effectively.
- A cuvette, which is a small, transparent container to hold the sample solution.
- A detector, such as a photocell or photoresistor, to measure the intensity of the light that passes through the solution.
- A meter or digital display to show the reading as either absorbance or transmittance.
5. What are some important real-world applications of colorimetry?
Colorimetry is a versatile technique with numerous applications across various fields, including:
- Environmental Science: Used in water quality testing to measure the concentration of pollutants like chlorine, fluoride, and nitrates.
- Medical Diagnostics: To determine the concentration of haemoglobin in blood samples or analyse other biological fluids.
- Food Industry: For quality control and to determine the concentration of specific compounds in food and beverages.
- Manufacturing: In the paint and textile industries to ensure colour consistency and quality.
- Agriculture: To analyse soil samples for essential nutrients like phosphorus and ammonia.
6. How does a colorimeter differ from a calorimeter?
Although their names sound similar, a colorimeter and a calorimeter measure entirely different properties. A colorimeter measures the absorbance of light by a solution to determine its concentration. In contrast, a calorimeter is an instrument used in thermodynamics to measure the amount of heat released or absorbed during a chemical reaction or physical change (enthalpy).
7. What is the main difference between colorimetry and spectrophotometry?
The primary difference lies in their precision and the way they select light. A colorimeter uses coloured filters to isolate a broad range of wavelengths. A spectrophotometer uses a monochromator (a prism or grating) to select a very narrow, specific wavelength of light. This makes spectrophotometry more accurate, versatile (covering UV, Visible, and IR spectrums), and capable of more detailed analysis than colorimetry, which is generally simpler and less expensive.
8. How are absorbance and transmittance related in colorimetry?
Absorbance and transmittance are inversely and logarithmically related. Transmittance (T) is the fraction of the original light that passes through the sample (T = I/I₀). Absorbance (A) is the amount of light absorbed by the sample. The relationship is given by the formula A = -log₁₀(T). If a sample has 100% transmittance (no light absorbed), its absorbance is 0. If it has 10% transmittance, its absorbance is 1.
9. Why is it necessary to use a “blank” solution in a colorimetry experiment?
A "blank" solution, which is typically the pure solvent used to prepare the sample, is essential for calibrating the colorimeter. It is used to set the instrument's absorbance reading to zero (or transmittance to 100%). This step ensures that any measurement taken afterwards is due solely to the solute and not from the absorbance of the solvent, scratches on the cuvette, or other background interferences. This process is crucial for obtaining accurate results.
10. Under what conditions might the Beer-Lambert law fail or show deviations?
The Beer-Lambert law is highly effective but can show deviations from its expected linear relationship under certain conditions. Key reasons for failure include:
- High Concentrations: At high concentrations, solute particles can interact with each other, which alters their ability to absorb light, causing a non-linear response.
- Instrumental Limitations: The law strictly applies to monochromatic light. If the light source is not purely one wavelength, deviations can occur. Stray light reaching the detector also causes errors.
- Chemical Changes: If the solute undergoes a chemical reaction, dissociation, or association in the solvent, its concentration and light-absorbing properties change, leading to inaccurate readings.
