How does an UV-Vis detector work?

Operating Principle of a UV-Vis Detector

Ultraviolet-visible (UV-Vis) spectroscopy is a widely used analytical technique for the quantitative and qualitative analysis of various substances. A key component of this method is the UV-Vis detector, which measures the intensity of light in the ultraviolet and visible regions of the electromagnetic spectrum as it passes through a sample.

How It Works

The UV-Vis detector starts with a light source, typically a deuterium lamp for the ultraviolet region and a tungsten-halogen lamp for the visible region, which emits light that covers the UV and visible spectrum.

Next, the light passes through a monochromator, a device that isolates a narrow band of wavelengths. This monochromatic light then proceeds to the sample.

When the monochromatic light reaches the sample, some of it is absorbed while the rest passes through. The amount of light absorbed depends on the concentration of the absorbing species in the sample based on Beer-Lambert's law.

The transmitted light finally reaches the detector, which measures its intensity. A decrease in light intensity indicates absorption by the sample. These measurements are compared to those of a reference beam that bypasses the sample, allowing for accurate determination of the sample's absorbance.

The detector converts these light intensity measurements into electrical signals, which are then processed and displayed as an absorbance spectrum on an output display. This spectrum provides valuable information about the molecular composition and concentration of the sample.


  • Quantitative analysis of pharmaceutical compounds.
  • Determination of organic or inorganic species in water.
  • Measurement of reaction kinetics.
  • Quality control in various industries.

In summary, the UV-Vis detector plays a crucial role in spectroscopy by allowing the measurement of the absorbance of light, thereby providing insights into the chemical composition and concentration of substances in a sample.

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