Limitations of colorimetry


  • Spectrophotometer vs. Colorimeter: What’s the Difference?
  • What are the benefits of using a colorimeter?
  • In terms of chemical analysis, it is, more specifically, the measurement of the concentration of a particular compound solute in a colored solution solvent. During scientific work, we often need to measure quantities of a particular compound in a mixture or the concentration of the solution. The trick is to identify the difference in colors of various mixtures and ascertain their absolute values.

    This is more informative and scientifically useful than simply having subjective judgments such as solutions being light or dark in color.

    Our eyes are not good enough to distinguish finer differences in colored solutions! Light in the form of electromagnetic radiation enables a human eye to visualize objects. Visible light is measured in terms of wavelengths in the range of nm. Scientists have identified that the human eyes have 3 different types of cone cells which helps perceive color. This phenomenon is called Trichromacy. In order to create different colors, a human eye needs three different wavelengths of light; blue short range , green medium range , and red long range.

    There is a threshold beyond which the human eyes are not sensitive enough to distinguish small changes in the colors of a solution. Therefore, there is a need for a more sensitive measuring instrument which could give reliable and consistent results. This instrument is known as a Colorimeter. In determining the concentration of a solute in a solution, the Beer-Lambert law is used.

    The Beer-Lambert law The first criterion for measuring the amount of solute in a given solvent is that the solution must be homogeneous. When a ray of light passes through the solution, a part of the light radiation is absorbed by the solution.

    The amount of light absorbed and transmitted is defined by the Beer-Lambert law. This law is actually a combination of two different laws i. Beer-Lambert law only holds true in the following scenarios; The light passing through the sample must be monochromatic of a single wavelength.

    The solution must be homogeneous. If not, at high concentrations, the molecules may aggregate and this would lead to incorrect readings. The solution must not have a molecule that emits fluorescence when excited. If it does, then this can lead to erroneous readings. The temperature of the solution must not change, as the molar extinction coefficient depends on it. The Components of a Colorimeter The Colorimeter is the instrument used to ascertain the concentration of a solution by measuring the amount of absorbed light of a specific wavelength.

    One of the earliest and popular designs, Duboscq Colorimeter, invented by Jules Doboscq, dates back to the year This is made either of glass, quartz, or plastic. These are made of light sensitive material such as selenium. How does the Colorimeter work? Having discussed the principles and components of a Colorimeter, it is time to look into the functionality of a colorimeter, as follows; The process starts with white light being emitted from the LED or tungsten lamp.

    This light is passed through a slit and is focussed into a parallel beam by a condenser lens. This beam passes through a series of lenses, which focuses a particular wavelength of light on the solution. The solution under question is held in a cuvette of a given path length width of the cuvette.

    A part of the light is absorbed and the rest is transmitted from the solution. These readings can be obtained within a second. Important considerations about the above method for getting optimal results Sample container should be made of glass or plastic for visible range of light and of quartz for U. V range. This is because glass absorbs U.

    V radiation. The wavelength at which maximum absorption occurs, for the solution in question, should be selected for the analysis. It has been shown experimentally that the absorbance at this wavelength is more stable than at other wavelengths. The samples should be adequately diluted to avoid high absorbance value which could lead to incorrect estimation of the concentration. Stray light, either emerging from within the colorimeter due to an issue with the optics or from outside due to inadequate sealing would influence the reading in the meters.

    Standard solutions for finding unknown concentrations A point to note is that the value obtained in the meter does not have any meaning since it is coming from a solution having an unknown concentration. We cannot translate that value into a concentration value because we do not have a pre-set reference.

    In order to identify the concentration of the solution, we need to quantify a standard of known concentrations. Standard solutions of various known concentrations are prepared and the absorbance is observed for each solution.

    A standard curve is drawn with these values, usually with absorbance on the Y axis and the concentration of the solution on the X axis. Using this method, the transmittance value for the solution can be used to extrapolate its concentration. Uses of a Colorimeter in the real world Colorimeters are widely used for monitoring the growth of bacterial or yeast cells in liquid cultures. They are used for quarantine purposes in the food industry where the color of food and beverages are monitored.

    Color additives are often added to food as a compensation for the loss of natural color of the food due to exposure to light and air. It is important to ensure that these artificial colors are of adequate amount to ensure health and safety. They are used to detect plant nutrients in the soil. They are used to screen chemicals in water such as chlorine, nitrite, fluoride, cyanide, iron etc.

    Is there a better Instrument than the Colorimeter? The spectrophotometer is the answer to that question. A spectrophotometer is like a colorimeter, in that it is also used in studying colored solutions, however, it is a bit more advanced. The Colorimeter, no doubt, is a fast, inexpensive way to quantitate solutes in a solution. However, like all techniques, this instrument also has some drawbacks, as follows; A wide range of wavelengths cannot be used in colorimetry, as the colorimeter is restricted to only a few wavelengths.

    The spectrophotometer, on the other hand, uses a monochromator instead of filters and it can be used in Ultra Violet UV and Infra-red IR wavelength as well. Therefore, the spectrophotometer provides more precision in terms of the wavelengths being used for analysis. Spectrophotometers are more precise and accurate than colorimeters. Both colored and colorless solutions can be analyzed in spectrophotometers, whereas only colored solutions can be analyzed in colorimeters.

    Other related Instruments to a Colorimeter Densitometer: This device is used for quality control of colors in a printed material. It is also used for medical diagnosis, where human tissues are exposed to radio-labeled ligand.

    Technological advancements make the Colorimeter more convenient As technology progresses, so does the technical advancements in the field of colorimetry.

    There are now more sophisticated colorimeters than the Duboscq Colorimeter. Also, there now exists a smartphone app to do colorimetry, making the process more convenient and inexpensive. Conclusion Colorimetry is a very quick and efficient way of analyzing colored solutions or any colored substance.

    Decades of research has enabled development of high end colorimeters which are more precise and convenient to use. The immense potential of colorimetry in terms of applications ranging from food, textiles, soil, and scientific research proves that this technique will not be getting redundant any time soon.

    References C. Oleari, Standard colorimetry: definitions, algorithms, and software, Wiley, West Sussex, England, Sliney, What is light? The visible spectrum and beyond, Eye Lond. Lee, The evolution of concepts of color vision, Neurociencias, 4 Brown, G.

    Swinehart, The Beer-Lambert law, J. Educ, 39 Mantele, E. Anzalone, A. Glover, J. Pearce, Open-source colorimeter, Sensors Basel , 13 Settle, Chemical instrumentation, evolution of instrumentation for UV- visible spectrophotometry, J.

    Choudhuty, Color measurement instruments, Principles of Color and Appearance Measurement, Wen, S. Zhou, J. Chen, Colorimetric detection of Shewanella oneidensis based on immunomagnetic capture and bacterial intrinsic peroxidase activity, Sci Rep, 4 Popov-Raljic, J. Mastilovic, J. Lalicic-Petronijevic, V. Popov, Investigations of bread production with postponed staling applying instrumental measurements of bread crumb color, Sensors Basel , 9 Lalicic-Petronijevic, Sensory properties and color measurements of dietary chocolates with different compositions during storage for up to days, Sensors Basel , 9 Liu, L.

    Tao, B. Liu, X. Tian, M. Mohammad, Y.

    Spectrophotometer vs. Posted on by Ken Phillips Color surrounds us every moment of our lives and affects our emotions, behaviors and beliefs in large and small, conscious and unconscious ways.

    Color can set a mood, warn us of danger, give us critical information and even bring us joy. Despite the universal presence of color, describing it remains elusive, in part due to variations in color perception from person to person and in part due to a lack of descriptors for each of the millions of shades seen by the human eye.

    Instrumental color measurement moves beyond the limits of human perception and vocabulary and allows us to capture color information as objective data, creating a common language of color that is essential for communication within and between industries around the world.

    The two most advanced color measurement instrument types are colorimeters and spectrophotometers, both of which use sophisticated technologies to accurately and precisely quantify and define color.

    While closely related, these instruments have unique qualities that may make one more suitable than the other for a particular type of measurement. Understanding the characteristics of a colorimeter vs.

    What Is a Colorimeter? A colorimeter is designed to perform a type of psychophysical sample analysis, which means its measurements correlate to human perception. In other words, it is designed to see color the way we do.

    Its results are direct and read as tristimulus values. A tristimulus value is one that identifies a color with characters that represent different dimensions of its visual appearance. A tristimulus value may contain values like X, Y and Z or L, a and b. There are a few unique components involved in a colorimeter. Illuminant: The illuminant represents a specific light source, such as daylight or incandescent light, to project consistent brightness onto the object.

    In a colorimeter, an illuminant is fixed. Observer: The standard observer offers a specific field of view with which to analyze the colors.

    A colorimeter usually uses a 2-Degree Standard Observer, which is suitable for color evaluation and quality control. Tristimulus absorption filter: The absorption filter isolates specific wavelengths to be applied to the sample. The colorimeter starts with a simple light source.

    With the help of a lens and tristimulus absorption filters, the beam of light becomes a single, focused wavelength which then moves through to the sample solution.

    On the other side of the solution is a photocell detector that identifies how much of the wavelength got absorbed. The detector is connected to a processor and digital display that offers a readable output of the results. The Pros of Colorimeter Below are some of the benefits of a colorimeter.

    They focus on tristimulus values. They tend to be more portable. Colorimeters are less complex, so they may be easier to move around or use in the field.

    They work quickly. Many applications for colorimeters require fast-moving equipment, such as on an assembly line, and a colorimeter can do that. The Cons of Colorimeters While the advantages of a colorimeter are clear, there are a few disadvantages associated with them.

    Colorimeters lack versatility, as their primary purpose is to compare products to a predefined sample. Metamerism occurs when colors look identical in one lighting condition, but not another.

    For instance, fluorescent lighting may make a product look quite different than it would in the sunlight. Applications for Colorimeters Typically, the colorimeter compares results to an existing sample.

    Colorimeters are extraordinarily accurate for straightforward color measurement and ideally suited for determination of color difference, fastness and strength as well as routine comparisons of similar colors. As such, they can be invaluable for color quality control and are primarily used in the production and inspection phases of manufacturing.

    What Is a Spectrophotometer? A spectrophotometer is an instrument designed for physical sample analysis via full spectrum color measurement.

    If desired, spectrophotometers can be used to calculate psychophysical colorimetric information as well. Spectrophotometers are incredibly precise and offer an expansive range of data. They use similar components to a colorimeter but with slight variations. Illuminant: The illuminant of a spectrophotometer is versatile. You can use standard and fluorescent illuminants that represent various types of light. Observer: The observer of a spectrophotometer is typically larger, at about 10 degrees.

    CIE recommends it as the most appropriate tool for industrial color applications. Prism, grating or interference filter: To isolate specific wavelengths, a spectrophotometer uses a prism, grating or interference filter, which allows it to change which wavelength gets selected. How Does a Spectrophotometer Work? The basic layout of a spectrophotometer is similar to a colorimeter, but with more steps and variations, as well as some different components. An illuminant projects a light source onto an object and through a prism, grating or filter.

    The tool used will isolate just one wavelength band to hit the sample. It can detect things like reflectance, transparency and illuminance along with a tristimulus value. Pros of a Spectrophotometer Some of the advantages of a spectrophotometer are as follows. They are incredibly comprehensive. They are versatile. You can typically adjust illuminance and observer settings to get just the right options on a spectrophotometer.

    They work with powerful software. By integrating with software, spectrophotometers offer a new, comprehensive way to review and analyze data outside of a built-in display. They come in a variety of styles. Spectrophotometers are available for a wide array of sample types, including powders, liquids and transparent materials.

    Portable options are also available. Cons of a Spectrophotometer Of course, no piece of technology is without a few drawbacks. Here are a few cons of spectrophotometers. They are more complex.

    With complexity comes sensitivity, and they may not be as suited for factory environments. They can be more expensive. Though price varies by model, spectrophotometers and their precise, broad range of information typically cost more than a colorimeter.

    They may have more technology than necessary. If you only need simple color measurements that a colorimeter can provide, a spectrophotometer may be more than you need. In the past, spectrophotometers have been large and complicated, but modern technology allows them to be smaller and more user-friendly.

    As such, spectrophotometers are capable of measuring metamerism, identifying colorant strength, analyzing a comprehensive range of sample types and giving users a choice between including or excluding specular reflectance to account for geometric attributes.

    Full-spectrum analysis also provides for greater specificity, potentially identifying color differences missed by colorimeters. Spectrophotometric instruments are ideally suited for a broad range of applications in the research and development phase, including color formulation and color system development , as well as color quality control throughout production.

    There are several similarities between colorimeters and spectrophotometers, but the two are still vastly different. The biggest difference is in capability and usage.

    Spectrophotometers are incredibly powerful and can offer more in-depth measurements than a colorimeter, such as spectral data.

    This is why they are primarily used for precise measurements in research and development or laboratory use. Colorimeters, in comparison, are simpler and are common in production and manufacturing, such as for quality control.

    A spectrophotometer is an instrument designed for physical sample analysis via full spectrum color measurement. If desired, spectrophotometers can be used to calculate psychophysical colorimetric information as well. Spectrophotometers are incredibly precise and offer an expansive range of data. They use similar components to a colorimeter but with slight variations.

    Illuminant: The illuminant of a spectrophotometer is versatile. You can use standard and fluorescent illuminants that represent various types of light.

    Observer: The observer of a spectrophotometer is typically larger, at about 10 degrees. CIE recommends it as the most appropriate tool for industrial color applications. Prism, grating or interference filter: To isolate specific wavelengths, a spectrophotometer uses a prism, grating or interference filter, which allows it to change which wavelength gets selected. How Does a Spectrophotometer Work? The basic layout of a spectrophotometer is similar to a colorimeter, but with more steps and variations, as well as some different components.

    An illuminant projects a light source onto an object and through a prism, grating or filter. The tool used will isolate just one wavelength band to hit the sample.

    It can detect things like reflectance, transparency and illuminance along with a tristimulus value. Pros of a Spectrophotometer Some of the advantages of a spectrophotometer are as follows.

    They are incredibly comprehensive. They are versatile. You can typically adjust illuminance and observer settings to get just the right options on a spectrophotometer. They work with powerful software. By integrating with software, spectrophotometers offer a new, comprehensive way to review and analyze data outside of a built-in display.

    They come in a variety of styles. Spectrophotometers are available for a wide array of sample types, including powders, liquids and transparent materials. Portable options are also available. Cons of a Spectrophotometer Of course, no piece of technology is without a few drawbacks. Here are a few cons of spectrophotometers. They are more complex. This is made either of glass, quartz, or plastic.

    These are made of light sensitive material such as selenium. How does the Colorimeter work? Having discussed the principles and components of a Colorimeter, it is time to look into the functionality of a colorimeter, as follows; The process starts with white light being emitted from the LED or tungsten lamp.

    Spectrophotometer vs. Colorimeter: What’s the Difference?

    This light is passed through a slit and is focussed into a parallel beam by a condenser lens. This beam passes through a series of lenses, which focuses a particular wavelength of light on the solution. The solution under question is held in a cuvette of a given path length width of the cuvette.

    A part of the light is absorbed and the rest is transmitted from the solution. These readings can be obtained within a second. Important considerations about the above method for getting optimal results Sample container should be made of glass or plastic for visible range of light and of quartz for U.

    V range. This is because glass absorbs U. V radiation. The wavelength at which maximum absorption occurs, for the solution in question, should be selected for the analysis. It has been shown experimentally that the absorbance at this wavelength is more stable than at other wavelengths.

    The samples should be adequately diluted to avoid high absorbance value which could lead to incorrect estimation of the concentration. Stray light, either emerging from within the colorimeter due to an issue with the optics or from outside due to inadequate sealing would influence the reading in the meters. Standard solutions for finding unknown concentrations A point to note is that the value obtained in the meter does not have any meaning since it is coming from a solution having an unknown concentration.

    We cannot translate that value into a concentration value because we do not have a pre-set reference. In order to identify the concentration of the solution, we need to quantify a standard of known concentrations. Standard solutions of various known concentrations are prepared and the absorbance is observed for each solution.

    A standard curve is drawn with these values, usually with absorbance on the Y axis and the concentration of the solution on the X axis. Using this method, the transmittance value for the solution can be used to extrapolate its concentration. Uses of a Colorimeter in the real world Colorimeters are widely used for monitoring the growth of bacterial or yeast cells in liquid cultures. They are used for quarantine purposes in the food industry where the color of food and beverages are monitored.

    Color additives are often added to food as a compensation for the loss of natural color of the food due to exposure to light and air. It is important to ensure that these artificial colors are of adequate amount to ensure health and safety.

    What are the benefits of using a colorimeter?

    They are used to detect plant nutrients in the soil. They are used to screen chemicals in water such as chlorine, nitrite, fluoride, cyanide, iron etc. Is there a better Instrument than the Colorimeter? The spectrophotometer is the answer to that question. A spectrophotometer is like a colorimeter, in that it is also used in studying colored solutions, however, it is a bit more advanced.

    The Colorimeter, no doubt, is a fast, inexpensive way to quantitate solutes in a solution. However, like all techniques, this instrument also has some drawbacks, as follows; A wide range of wavelengths cannot be used in colorimetry, as the colorimeter is restricted to only a few wavelengths. The spectrophotometer, on the other hand, uses a monochromator instead of filters and it can be used in Ultra Violet UV and Infra-red IR wavelength as well.

    Therefore, the spectrophotometer provides more precision in terms of the wavelengths being used for analysis. Spectrophotometers are more precise and accurate than colorimeters. Both colored and colorless solutions can be analyzed in spectrophotometers, whereas only colored solutions can be analyzed in colorimeters.

    Other related Instruments to a Colorimeter Densitometer: This device is used for quality control of colors in a printed material. It is also used for medical diagnosis, where human tissues are exposed to radio-labeled ligand.

    What are the advantages and disadvantages of colorimeter? 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.

    What is the principle of colorimetry? A colorimeter is a light-sensitive device used for measuring the transmittance and absorbance of light passing through a liquid sample.

    The device measures the intensity or concentration of the color that develops upon introducing a specific reagent into a solution. What are the basic principles of colorimetry? What is more accurate than a colorimeter? Spectrophotometers are incredibly powerful and can offer more in-depth measurements than a colorimeter, such as spectral data.

    This is why they are primarily used for precise measurements in research and development or laboratory use. Which is better spectrophotometer or colorimeter? A spectrophotometer has high precision and increased versatility.

    It is suitable for more complex color analysis because it can determine the spectral reflectance at each wavelength. However spectrophotometers can be more expensive than colorimeters. What are the advantages and disadvantages of colorimetry?

    Another advantage of colorimetry is that it is a portable system you can easily carry and transport. Disadvantages of colorimetry: The major disadvantage of colorimetry is that colorless compounds cannot be analyzed.


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