Difference Between Colorimeter and Spectrophotometer

Colorimeter vs Spectrophotometer
 

Colorimeter and spectrophotometer are the equipments used in colorimetry and spectrophotometry. Spectrophotometry and colorimetry are techniques, which can be used to identify the molecules depending on their absorption and emission properties. This is an easy technique to determine the concentration of a sample, which has a color. Though the molecule doesn’t have a color, if we can make a colored compound from it by a chemical reaction, that compound can also be used in these techniques. Energy levels are associated with a molecule, and they are discrete. Therefore, discrete transitions between the energy states will only occur at certain discrete energies. In these techniques, the absorption and emission arising from these changes in the energy states are measured and, this is the basis of all spectroscopic techniques. In a basic spectrometer, there is a light source, absorption cell and a detector. The radiation beam of the tunable light source passes through the sample in a cell, and the transmitted intensity is measured by the detector. Variation of the signal intensity as the frequency of the radiation is scanned is called the spectrum. If the radiation doesn’t interact with the sample, there won’t be any spectrum (flat spectrum). In order to record a spectrum, there has to be a difference in population of the two states involved. On a microscopic scale, the ratio of the equilibrium population in two states separated by an energy gap of ∆E is given by the Boltzmann distribution. The absorption laws, in other words Beer’s and Lambert’s laws, indicate the extent to which the intensity of the incident beam is reduced by the light absorption. Lambert’s law states that the degree of absorption is proportional to the thickness of the sample, and the Beer’s law states that the degree of absorption is proportional to the concentration of the sample. The principle behind the spectrophotometry and the colorimetry are the same.

Colorimeter

There are few parts that are common to any colorimeter. As a light source, normally a low filament lamp is used. In the colorimeter, a set of color filters are there, and according to the sample we are using, we can choose the required filter. Sample is placed in a cuvette, and there is a detector to measure the transmitted light. There is a digital or an analogue meter to display the output.

Spectrophotometer

Spectrophotometers are designed to measure the absorption, and they compose of a light source, a wavelength selector, cuvette and a detector. Wavelength selector only permits the selected wavelength to pass through the sample. There are different types of spectrophotometers as UV-VIS, FTIR, atomic absorption, etc.

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