UV Spectroscopy: Definition, Principle, Steps, Parts, Uses

What is UV Spectroscopy?

Spectroscopy refers to the measurement as well as study of electromagnetic radiation consumed or emitted as molecules, atoms, or ions in a sample shift from one energy level to another. In UV spectroscopy, a kind of absorption spectroscopy, a molecule collects light in the ultra-violet region (200–400 nm), which causes the electrons to be stimulated to an elevated energy state.

Principle of UV Spectroscopy

  1. Basically, spectroscopy deals with how light and matter interact.
  2. The amount of energy possessed by atoms or molecules. increases when light is absorbed by matter.
  3. Absorption of UV light results in the stimulation of electrons from their ground state to a higher energy state.
  4. By absorbing UV light, molecules having n-or-electrons may stimulate these electrons to elevated anti-bonding orbitals.
  5. The greater the electron’s ability to absorb longer wavelengths of light, the more quickly it may be energised. The four kinds of transitions (π–π*, n–π*, σ–σ*, and n–σ*), may be arranged in the following order: σ-σ* > n-σ* > π-π* > n-π*
  6. A chemical substance’s ability to absorb UV light results in a distinctive spectrum that makes it easier to identify the component.

Instrumentation or Parts of UV Spectroscopy

Light Source

  • Tungsten filament lamps as well as hydrogen-deuterium lamps were also the most common and suitable light sources since they emit light over the whole UV spectrum.
  • Whenever the performance of Hydrogen-Deuterium lamps is less than 375 nm, tungsten filament lamps release an excess of red radiation, especially radiation with a wavelength of 375 nm.


  • Prisms and slits are the most common components found in monochromators.
  • Double beam spectrophotometers make up the majority of the available models.
  • Rotating prisms are used to spread the radiation that the main source emits.
  • The slits then choose from among the numerous light source wavelengths that are separated by the prism, such that when the prism rotates, a sequence of wavelengths with steadily increasing intensities travels through the perforations for purposes of recording.
  • Using a second prism, the monochromatic beam selected via the slit is divided into two beams.

Sample and reference cells

  • The sample solution is transmitted via one of the two beams, whereas the reference solution is supplied through the other beam.
  • The cells contain both the sample and the standard solution.
  • These cells are composed of quartz or silica crystals. Glass cannot be utilised for the cells because it also absorbs UV rays.


  • Typically, the UV spectroscopy detector consists of two photocells.
  • The sample cell’s beam is picked up by one of the photocells, while the reference cell’s beam is picked up by the second detector.
  • The radiation beam from the reference cell has a greater energy level than the beam from the sample cell. As a consequence, the photocells generate alternating or pulsating currents.


  • The amplifier accepts the photocells’ generated alternating current.
  • The amplifier is coupled to a small servo meter.
  • Since the power generated by photocells is often quite weak, the major purpose of the amplifier is to multiply the signals such that they are readable.

Recording devices

  • Typically, an amplifier is coupled to a pen recorder that is connected to a computer.
  • The computer generates the spectrum of the chosen molecule and records all the produced data.

Applications of UV Spectroscopy

Detection of Impurities

  • This is among the most effective methods for identifying contaminants in organic compounds.
  • Due to the sample’s impurities, additional peaks may be seen, and they can be compared to the characteristics of a typical raw material.
  • Additionally, the pollutants may be determined by analysing the absorbency at a certain wavelength.

Structure elucidation of organic compounds

It helps to clarify the structure of organic compounds by identifying heteroatoms and determining whether unsaturation is present or not.

  1. Utilizing UV absorption spectroscopy, substances that collect UV light may be quantified.
  2. When judging a product’s quality, UV absorption spectroscopy may be used to characterise the different kinds of UV-absorbing compounds. Identification is achieved by comparing the absorbed spectrum to the spectra of recognised compounds.
  3. This approach is utilised to evaluate whether or not a chemical has a functional group. The absence of a spectrum at a certain wavelength is considered evidence that a particular category does not exist.
  4. UV spectroscopy may similarly be utilised to examine the kinetics of a process. The reaction cell is subjected to ultraviolet (UV) light, which causes changes in absorbance that may be seen.
  5. Many medications are either available as raw materials or as finished products. They may be tested by preparing an appropriate drug solution in a solvent and detecting the absorbance at a particular wavelength.
  6. By creating the appropriate derivatives of these chemicals, it is possible to spectrophotometrically estimate the molecular weights of various substances.
  7. A UV spectrophotometer may function as an HPLC detector.


  • http://www.indiastudychannel.com/resources/146681-Principle-working-and-applications-of-UV-spectroscopy.aspx
  • https://www.slideshare.net/AlexaJacob1/uv-visible-spectroscopy-ppt
  • https://www.slideshare.net/manishpharma/application-of-uv-spectroscopy
  • https://medium.com/@ankur1857/principle-of-ultra-violet-uv-spectrophotometer-e6a1c435d258
  • https://en.wikipedia.org/wiki/Ultraviolet%E2%80%93visible_spectroscopy
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