Spectroscopy- principle, types, and applications

Spectroscopy is a scientific technique that helps in quantifying the structural and molecular composition of a sample depending on the absorption and emission of electromagnetic radiation by the sample. The absorption, emission, and reflection of electromagnetic radiation vary in different samples.

Spectroscopy is widely involved in various fields like chemistry, molecular biology, astronomy, nanotechnology, photobiology, and more.Visible/Ultraviolet (UV), Atomic absorption spectroscopy, Infrared spectroscopy, and Raman spectroscopy are predominantly used in various fields.

During spectroscopy, electromagnetic radiation of a specific wavelength is passed through the sample resulting in absorption or emission of electromagnetic radiation by the substances present in the sample.

In absorption, the sample absorbs energy from the light source while emission, the sample emits light of a different wavelength that differs from the source’s wavelength. Spectroscopy analysis is performed with the help of an instrument called a spectrophotometer.

Principle behind spectroscopy

Spectroscopy is based on the principle of Beer Lambert’s law. According to this law states, when a beam of monochromatic light is passed through the sample solution, the intensity of absorption is directly proportional to the path length of the light and the molar concentration of the solution and this is given by the equation


Where A is the Absorbance

ε is the molar absorption coefficient

C is the molar concentration

L is the optical path length

6 Major types of Spectroscopy

Spectroscopy can be classified into various types and that includes

1.Visible/Ultraviolet (UV)

UV/Vis spectroscopy is the most common and widely used spectroscopic method. This is an absorption or emission spectroscopy. Visible spectroscopy is based on the fact that atoms are capable of either emitting or absorbing visible light. In UV-Vis spectroscopy, light is passed through a sample at a specified wavelength in the UV or visible spectrum. UV spectroscopy is used to estimate the concentration of protein and DNA in the sample.

2.Atomic Emission Spectroscopy (AE)

AES measures the emission of radiation from atoms in excited states. This method utilizes the atoms excited from the heat of a flame for light emission which helps in the analysis.

3.Atomic absorption spectroscopy (AA)

Atomic absorption spectroscopy or AAS quantifies the absorption of electromagnetic radiation by well-separated neutral atoms, unlike AE spectroscopy, a flame of lower temperature is used so as not to excite the sample atoms in this method. This method is predominantly involved in the quantification of metallic substances. This is because it has greater sensitivity and accuracy when compared to other methods.

4.Infrared spectroscopy (IR)

It is a powerful tool used for a wide range of samples IR spectroscopy depends on the change in the dipole moment.IR spectroscopy is absorption spectroscopy that measures absolute frequencies at which a sample absorbs radiation.it is used for both qualitative and quantitative analysis. Infrared spectroscopy is expensive.

5.Raman spectroscopy

Raman spectroscopy depends on the change in polarizability of a molecule. Currently, there are six major types of Raman spectroscopy in use. Although the advantage of this method is that it requires little to no sample preparation. Raman spectroscopy is inexpensive and rapid when compared to IR spectroscopy.

6.Nuclear magnetic resonance spectroscopy

Nuclear Magnetic Resonance spectroscopy or (NMR) is an analytical chemistry technique that functions based on electromagnetic fields. This spectroscopy is used in quality control and research to determine the content and purity of a sample as well as its molecular structure. NMR spectroscopy enables quantitative analysis of mixtures containing known compounds.

Spectroscopy – uses and Applications

Spectroscopic analysis is highly informative and used for both qualitative and quantitative analysis. Hence it has wide industrial applications and plays a predominant role in research and development, the following is a list of common applications of spectroscopy

  • In proteomics, this technique helps in the characterization of proteins
  • In the pharmaceutical industry, Spectroscopy helps in the analysis of bioactive compounds and metabolites.
  • In the Agricultural Industry, spectroscopy is used as a nitrogen sensor and helps to estimate the concentration of nitrogen in rice.
  • It helps to detect contaminants and adulterants in the food industry
  • Spectroscopy also enables water quality testing
  • It helps to determine cell growth and viability in bacterial samples
  • In hospitals, it is helpful in the analysis of gas used for respiration in patients.
  • Spectroscopy is used to determine the structure and functional groups in organic compounds.
  • It helps to determine the presence of biomolecules
  • It is used to indicate the presence of toxins and pollutants in the environment
  • It is also involved in astronomical studies
  • Spectroscopy enables the detection of catalysis in a chemical reaction
  • It can also be used as a detector system for other analytic procedures like HPLC
  • Spectroscopy facilitates forensic studies as well.