Both colorimeter and spectrophotometer are the instruments used to measure the light-absorbing properties of substances. However, the two are differentiated in a way that a colorimeter measures the concentration of solute in any given solution by determining the absorbance of a specific wavelength of light passing through the solution. As against, a spectrophotometer measures the transmittance or reflectance of light by passing it through a sample solution.
The two operate in somewhat similar ways as both the instruments make use of solution and beam of light to check for the absorbance level of light however, various differences exist between the two. So, let us see what are those difference.
Content: Colorimeter Vs Spectrophotometer
Comparison chart
| Basis for Comparison | Colorimeter | Spectrophotometer |
|---|---|---|
| Basic function | Measuring light absorbance level | Measuring light transmittance level |
| Approach | Psychophysical analysis | Physical analysis |
| Sensitivity | Less | Comparatively more |
| Cost | Low | High |
| Complexity | Less complex and is generally rugged. | More complex |
| Parts | Stationary | Movable |
| Weight | Light | Comparatively heavy |
| Wavelength offered | Fixed, in visible range of spectrum | Wide range, in UV, visible and infrared range of spectrum |
| Provides | The obtained colorimetric data, provides tristimulus values. | The obtained data, indirectly provides psychophysical information. |
| Helpful in | Comparing same colour, colour difference adjustment. | Colour formulation, measures variable illuminant and metamerism condition. |
| Application | It determines the concentration of compound according to its absorbance level. | It identifies and quantifies organic and inorganic biochemical molecules. |
Definition of Colorimeter
Colorimeter is used to check the absorbance level of a specific wavelength of light through a given solution. It makes use of Beer-Lambert law to find the concentration of solute in a given solution.
The major elements that constitute colorimeter are:
- Source of light
- Filter
- Glass slab or chamber
- Photosensitive detector
- Galvanometer
In colorimetric test, a beam of light is passed through a coloured solution, the passing light is captured in a photocell to get the level of absorbance of the light by the solution. Before passing through the solution the light is passed through the filter which selects the desired wavelength of light. After filtering, the light is allowed to reach the photocell via a glass slab.
Colorimeters possess a wide range of uses chemically and biologically such as analyzing blood, soil nutrients, solution concentration, etc.
Definition of Spectrophotometer
A spectrophotometer is an instrument that measures the light-absorbing or transmitting ability of solutions when a beam of light is passed through it. The amount of light absorbed or transmitted by chemical solutions depends on the wavelength of light and the type of solution.
This device helps in the quantification of light which gets transmitted when falls on a solution. The spectrophotometer uses a lens system that focuses the light towards an open slit. This light is then focused towards an exit slit using a second lens so the monochromatic light coming out of the slit get split into its component wavelengths. This arrangement acts as a prism that splits the monochromatic light falling on it into its component wavelength.
Further, according to the requirement, the slit arrangement is rotated so as to get the desired wavelength that will be passed to the photocell. The photocell forms collection with the galvanometer which displays the transmittance value directly by taking the electrical output from the photocell.
The sample solution is present between the exit slit and the photodetector. In case there is a clear solution then the light will transmit completely through it. But as the solution becomes turbid, the level of transmittance decreases, hence the more dense the solution, the less will the transmittance.
Key Differences Between Colorimeter and Spectrophotometer
- Colorimeter is an instrument that measures the amount of transmitted ray of light absorbed by a specific solution. However, spectrophotometer measures the intensity of light as a function of colour or wavelength of light by the transmittance level.
- Colorimeter results in psychophysical analysis, offering colour measurement physically like the human eye and brain perception to visualize things. While spectrophotometer results in physical analysis through which colorimetric information can be gathered indirectly.
- Colorimeters are considered to be less sensitive instruments in comparison to spectrophotometers.
- Spectrophotometers are expensive than colorimeters.
- The design of colorimeter is less complex, is light in weight and is rugged in general thus suffers less wear and tear during operation while this is not the case with spectrophotometer as it comparatively heavy thereby exhibiting more complexity.
- Colorimeters have stationary parts while the parts of spectrophotometers are non-stationary.
- Colorimeters offer fixed wavelength, usually in the visible range of spectrum whereas spectrophotometers offer wide variable wavelength, ranging in UV, infrared and visible range.
- Tristimulus data is obtained from colorimetric analysis whereas colorimetric data can be obtained indirectly by spectrophotometric analysis.
- Through colorimetric test, colour comparison and colour difference adjustments can be done. While the spectrophotometer helps in colour formulation and measurement of the variable illuminant.
- According to the level of absorbance, the colorimeter determines the concentration of the compound. As against, the intensity of light helps in identifying organic and inorganic molecules.
Conclusion
From this discussion, it is clear that colorimeter and spectrophotometer are the two instruments that use the same principle of operation but one determines the concentration of solution while the other determines the intensity of light when passed through a solution.