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What is a Spectrophotometer?


Detecting a chemical compound without a spectrophotometer never being easy. That why every chemistry lab is equipped with this analytical device. Spectrophotometer works by separating the spectral of light and measure its component intensity. Since some chemicals absorb light thus the intensity of the adsorption can be measured by using a spectrophotometer and its concentration could be quantified.


Light is some sort of electromagnetic radiation emitted from its sources. It could be light from the candle, lamp, sunlight reflected by the moon, or any objects. Everything within our surrounding adsorbs and emits light. That why they exist in various colors. Banana looks yellow when ripe because they absorb other light colors and only emitting yellow light. The light that we see is called visible light.

The chemical compound absorbs light

Colored chemical can be measured with spectrophotometer
Image by Bokskapet from Pixabay

Some chemical compounds are able to absorb and only emits a specific light color within the visible light region. That how they appear colored because the rest of the colors are filtered. If the compound does not absorb light, it will appear colorless if it transmits the light like water, or white if it reflects the light. Thus, the concentration of any chemicals that capable to absorb light can be measured according to the intensity of the light absorbed.

Basic working principle of spectrophotometer

The spectrophotometer is using a prism mechanism where the white light source is separated into a wide spectrum of visible colors including ultraviolet. The basic diagram of the spectrometer consists of a light source, light dispersion device (works like a prism), wavelength selector, sample chamber, and detector. The source of light usually either from tungsten halogen lamp (UV light), deuterium arc lamp (Visible light), or xenon arc lamp (UV-Vis light). The light produced can be polarized within the UV (200 – 400 nm) and visible light (400 nm to 750 nm) governed by the type of light source and light dispersion device.

A specific wavelength is selected before the analysis by the wavelength selector. The chosen wavelength usually absorb most by the chemical compound to be analyzed to maximize the accuracy of the quantification. The light is directed to pass through the liquid sample in a cuvette in the sample chamber. The intensity of the light pass through the sample is measured by the light detector. Usually, a concentrated solution will absorb more light compared to a diluted solution. Thus, the intensity of the light should be reduced after pass through the liquid sample.

The spectrophotometer has been very useful in the scientific field, especially for chemists, biologists, biochemists, and engineers.


  1. Absorption of Light by Organic Molecules
  2. Light: Electromagnetic waves, the electromagnetic spectrum and photons
  3. What is a Spectrometer
  4. How Do We See Color