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Spectroscopy Types and Techniques

Stacy Pirro, Nicola McDougal
  • Author
    Stacy Pirro

    Stacy Pirro has taught courses in biology, animal science, bioinformatics, microbiology, mathematics, entomology and ecology for 17 years. She has a Ph.D. in Molecular Biology from the Animal Science department at the University of Massachusetts.

  • Instructor
    Nicola McDougal

    Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

Learn what spectroscopic analysis is. Identify how types of spectroscopy are classified, and discover practical applications of various spectroscopic techniques. Updated: 03/27/2022

Spectroscopy: Definition

Spectroscopy is the study of the interaction of electromagnetic waves and matter. It normally involves using a specialized piece of equipment called a spectrometer to record the wavelength of electromagnetic radiation to get information about the structure and other properties of the sample. Materials with different properties and structures will emit different colors and wavelengths as light passes through. These wavelengths are compared against known standards to determine the material's composition.


Electromagnetic spectrum

Electromagnetic spectrum


Inside an Analytical Lab

TV and filmmakers love chemical analysis. I am sure you instantly recognize the labs in shows like CSI, Bones and NCIS. These labs are filled with all sorts of instruments, and the scientists are painstakingly analyzing the information that comes out of them. Unlike TV, where just one piece of analysis coming from one instrument instantly solves the crime, in real life, scientists need many different types of chemical analysis. Each lab instrument provides a different piece of information to help solve the puzzle. In this lesson, we are going to learn about the important topic of spectroscopy, which is a scientific technique for analyzing the properties of material by measuring its interaction with light.

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  • 0:50 Electromagnetic Radiation
  • 2:30 The Spectrometer
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Types of Spectroscopy

There are three basic types of spectroscopy: atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), and atomic fluorescence spectroscopy (AFS). Different methods of spectroscopy may be employed depending on the type of sample and analysis needed.

1. Atomic Absorption Spectroscopy (AAS)

  • Infrared spectroscopy measures the composition of matter by the light that is absorbed, reflected, or emitted. This method is used to identify the chemical composition of a sample based on the functional groups identified by the resulting spectra. Each chemical functional group has a known spectrum, and the analysis of the entire spectrum of the sample allows the reconstruction of the molecular structure based on the data of each component. The instrument used for this type of analysis is called an infrared spectrometer.
  • Ultraviolet-visible spectroscopy is used to analyze the target sample by measuring visible and ultraviolet light emissions. The emissions in the visible light of the electromagnetic spectrum affect the color of the compound. This method is based on the principle that the range of the electromagnetic spectrum measures transitions in the state of the electrons in the compound. Molecules of the target compound absorb energy emitted by the spectrometer, which moves their electrons to a higher orbital. The lower the initial orbital of the electrons, the longer the wavelength of light it can absorb. The composition of the light emitted at each wavelength is measured by the spectrophotometer and used to identify and analyze the sample. This type of analysis is most commonly used for biological macromolecules and inorganic compounds in a liquid solution.

2. Atomic Emission Spectroscopy (AES)

  • Nuclear magnetic resonance spectroscopy measures the local magnetic fields around the nuclei of atoms. The target sample is analyzed by first placing it in a magnetic field, followed by exciting the nuclei using radio waves. This causes the nuclei to reach a state of nuclear resonance, which allows the device to measure the interaction of the nuclear spins in the target's atoms. The resulting signals are captured by the spectrometer and provide information on the atomic composition of the sample and the functional groups of the molecules. NMR spectroscopy is most commonly used with biochemical compounds, such as proteins. One advantage of this method is that only a small sample is required, and this makes it valuable in medical applications in which only a small clinical sample is available.


The NMR spectrum of ethanol

The NMR Spectrum of Ethanol


3. Atomic Fluorescence Spectroscopy (AFS)

  • Raman spectroscopy is used to analyze the vibrational fingerprints of molecules and identify the molecular structure of the target compound. Raman spectroscopy involves Raman scattering, which is the inelastic scattering of photons. To perform this function, the spectrometer focuses a beam of monochromatic light through the sample. The light source is typically produced by a laser, although X-rays are used for some applications. The light produced by the laser excites the molecules in the sample, and the resulting molecular vibrations are recorded by the device's detector. The pattern of energy changes in the laser's photons is compared to a set of standards and used to identify the sample. This method is often used in conjunction with infrared spectroscopy to yield complementary information and identify similar samples with greater accuracy.
  • X-ray spectroscopy is used to analyze materials by analyzing their interaction with the X-ray part of the electromagnetic spectrum. This method measures the change in the energy level of inner-orbital electrons when excited by photonic energy. This causes electrons to temporarily move to an outer orbital shell. When the electrons return to their original lower shell, they release energy in a spectrum characteristic of their atomic structure. This energy is detected and recorded by the spectrometer and used to identify the atomic composition of the structure. Some elements emit multiple characteristic wavelengths as the result of this process. The raw data is typically corrected for atomic number, fluorescence, and absorption characteristics prior to the final analysis, which produces both qualitative data used for identification and quantitative data used to measure how much of each element is present.

X-ray spectra from all known elements are available for use as references, allowing a complete analysis from the entire periodic table.

Electromagnetic Radiation

We are going to look at four techniques commonly used to help with structural analysis: ultraviolet-visible spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry. The first three are known as absorption spectroscopy, and we will deal with these first.

Spectroscopic techniques involve absorption of specific energies of light or, more accurately, electromagnetic radiation. Absorption, here, simply means that energy has been transferred from the radiation to the molecule. This energy change causes a transition or an excitation from a lower energy level to a higher energy level. Each absorption corresponds exactly in energy to a very specific excitation depending on the wavelength of the light. If we understand these excitations, then we can begin to figure out the structural features of that molecule.

The electromagnetic spectrum
The electromagnetic spectrum

Here we have the electromagnetic spectrum. You can see the different types of radiation, from radio waves on the left at low energy all the way through to gamma rays on the right at very high energy. The radiation we are interested in here, is ultraviolet and visible, infrared and, finally, radio waves for NMR.

So how do we use electromagnetic waves to help us analyze material? Great question! Let's move on and see how data is acquired using a spectrometer.

The Spectrometer

We have just learned that spectroscopy involves the absorption of specific energies of electromagnetic radiation. All types of absorption spectrometers share common features. The radiation source depends on the type of radiation being used, and the sample holder will vary depending on the sample being analyzed. Using a series of lenses and photocells, the spectrometer compares the electromagnetic radiation shining on the sample to the radiation that just passes through. This provides us with the output. The output can either be a number or a spectrum.

Let's have a quick look at a typical infrared spectrum. All absorption spectra provide two kinds of information that help us identify the chemical structure of a mystery material. The absorption wavelength, or frequency, gives the energy associated with a particular excitation. This can be related to a specific part of a molecule. For example, this helps us identify functional groups. And the absorption intensity provides information on both the ease of transition and the concentration of the absorbing part of the molecule. Hopefully, you can see that this information is starting to give us a fingerprint of the molecules contained in a given material. Using the information from different techniques can help us solve the mystery.

What Can Spectroscopy Tell You?

The development of spectroscopic methods of analysis has provided scientists with a tool kit to help identify complex unknown molecules.

And one of the most important advantages of spectroscopy is that it is non-destructive. This means that, if you are working on a crime scene, you are not destroying the evidence in the process of analyzing it! This is a huge plus. A court judge would be not happy if you told her you had destroyed something vitally important. For this reason, spectroscopic techniques are used before more damaging types of analysis.

Okay, so let's briefly look at the sort of information the different techniques can help us with. Ultraviolet-visible spectroscopy is hugely versatile. UV-visible radiation transfers the right amount of energy to cause electron transitions from the ground state to the excited state. It is particularly useful in the analysis of colored materials, such us dyes and paints. In forensic analysis, it is often used to identify pigments in textiles.

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Video Transcript

Inside an Analytical Lab

TV and filmmakers love chemical analysis. I am sure you instantly recognize the labs in shows like CSI, Bones and NCIS. These labs are filled with all sorts of instruments, and the scientists are painstakingly analyzing the information that comes out of them. Unlike TV, where just one piece of analysis coming from one instrument instantly solves the crime, in real life, scientists need many different types of chemical analysis. Each lab instrument provides a different piece of information to help solve the puzzle. In this lesson, we are going to learn about the important topic of spectroscopy, which is a scientific technique for analyzing the properties of material by measuring its interaction with light.

Electromagnetic Radiation

We are going to look at four techniques commonly used to help with structural analysis: ultraviolet-visible spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry. The first three are known as absorption spectroscopy, and we will deal with these first.

Spectroscopic techniques involve absorption of specific energies of light or, more accurately, electromagnetic radiation. Absorption, here, simply means that energy has been transferred from the radiation to the molecule. This energy change causes a transition or an excitation from a lower energy level to a higher energy level. Each absorption corresponds exactly in energy to a very specific excitation depending on the wavelength of the light. If we understand these excitations, then we can begin to figure out the structural features of that molecule.

The electromagnetic spectrum
The electromagnetic spectrum

Here we have the electromagnetic spectrum. You can see the different types of radiation, from radio waves on the left at low energy all the way through to gamma rays on the right at very high energy. The radiation we are interested in here, is ultraviolet and visible, infrared and, finally, radio waves for NMR.

So how do we use electromagnetic waves to help us analyze material? Great question! Let's move on and see how data is acquired using a spectrometer.

The Spectrometer

We have just learned that spectroscopy involves the absorption of specific energies of electromagnetic radiation. All types of absorption spectrometers share common features. The radiation source depends on the type of radiation being used, and the sample holder will vary depending on the sample being analyzed. Using a series of lenses and photocells, the spectrometer compares the electromagnetic radiation shining on the sample to the radiation that just passes through. This provides us with the output. The output can either be a number or a spectrum.

Let's have a quick look at a typical infrared spectrum. All absorption spectra provide two kinds of information that help us identify the chemical structure of a mystery material. The absorption wavelength, or frequency, gives the energy associated with a particular excitation. This can be related to a specific part of a molecule. For example, this helps us identify functional groups. And the absorption intensity provides information on both the ease of transition and the concentration of the absorbing part of the molecule. Hopefully, you can see that this information is starting to give us a fingerprint of the molecules contained in a given material. Using the information from different techniques can help us solve the mystery.

What Can Spectroscopy Tell You?

The development of spectroscopic methods of analysis has provided scientists with a tool kit to help identify complex unknown molecules.

And one of the most important advantages of spectroscopy is that it is non-destructive. This means that, if you are working on a crime scene, you are not destroying the evidence in the process of analyzing it! This is a huge plus. A court judge would be not happy if you told her you had destroyed something vitally important. For this reason, spectroscopic techniques are used before more damaging types of analysis.

Okay, so let's briefly look at the sort of information the different techniques can help us with. Ultraviolet-visible spectroscopy is hugely versatile. UV-visible radiation transfers the right amount of energy to cause electron transitions from the ground state to the excited state. It is particularly useful in the analysis of colored materials, such us dyes and paints. In forensic analysis, it is often used to identify pigments in textiles.

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Frequently Asked Questions

What is spectroscopy in simple terms?

Spectroscopy refers to several methods used to identify and analyze compounds based on their interaction with different wavelengths of the electromagnetic spectrum. These methods are based on atomic absorption, atomic emission, or atomic fluorescence.

What is spectroscopy used for?

Spectroscopy is used for a variety of medical and scientific applications. These include detection of pesticides in crops, analysis of the molecular components of petroleum products and determination of its origin, and clinical uses such as finding the source of poisoning in humans and animals.

What are the three basic types of spectroscopy?

The three basic types of spectroscopy are atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), and atomic fluorescence spectroscopy (AFS).

AAS includes methods such as infrared (IR) spectroscopy and ultraviolet-visible (UV-Vis) spectroscopy. AES includes nuclear magnetic resonance (NMR) spectroscopy and X-ray spectroscopy. AFS includes Raman spectroscopy.

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