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 Types and Techniques
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.
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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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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.
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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.
Spectroscopic Techniques
Spectroscopic techniques involve passing a beam of energy through a sample and recording and analyzing the results to determine the identity, composition, and quantities of the components of the sample. Samples analyzed in this way are typically in liquid stats, but in some applications, gasses or solids can be used. The type of energy used can vary depending on the type of sample and the type of data needed. Energy types used by spectroscopic methods range from visible light, infrared, photons, and X-rays.
These methods are often used in conjunction with other types of analysis, like mass spectrometry, which operates on different principles and is a destructive process.
Applications of Spectroscopic Analysis
Spectroscopic analysis is used in a wide variety of applications, including scientific, industrial, and medical research. Crop products such as wheat or corn are routinely analyzed to detect trace amounts of pesticides, ensuring the food is safe to eat. Disallowed pesticides have molecular structures that differ from safer pesticides cleared for use on food. These can be differentiated by spectroscopic analysis.
Petroleum products such as crude oil come from many places in the world. Oils from different regions differ in their chemical composition, and these differences can be determined by spectroscopic analysis. Oil from one well may contain a specific load of heavy metal compounds, such as cadmium, arsenic, and mercury salts, while other wells may contain these same compounds in different amounts or not at all. Spectroscopic data enables scientists to identify the region of origin, often with a high degree of resolution.
Instances of human or animal poisoning can be identified by spectroscopic analysis on blood or tissue samples drawn from the affected individual, providing valuable information on the source of the toxin. This can assist in the treatment of the patient or provide valuable insight to forensic investigators.
Lesson Summary
Spectroscopy involves the identification of a sample by recording how it interacts with certain types of energy. Different spectroscopic methods use different wavelengths of the electromagnetic spectrum as energy sources, and these different energy types cause different reactions in the atomic and molecular structure of the samples. For example, infrared radiation causes vibrational excitement of the bonds in the target molecules, and nuclear magnetic resonance spectroscopy uses radio waves as an energy source. Complimentary techniques include mass spectrometry, which is a destructive technique that produces quantitative evidence. There are three basic types of spectroscopy: 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. Different methods may also be employed for each type, depending on the type of sample and analysis needed. Spectrometry is used in scientific, industrial, and medical research for diverse applications, such as testing pesticides in crops, determining the chemical composition and origin of petroleum products, and determining the source of poisons in humans and animals.
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.
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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.
Infrared spectroscopy is used extensively in chemical and forensic labs. Infrared radiation transfers the right amount of energy to cause vibrational excitation of the bonds in the molecule. Infrared spectroscopy is used for a variety of forensic applications, including analysis of binders and additives in paint and the analysis of alcohol in blood.
Nuclear magnetic resonance (NMR) sounds a lot more sinister than it really is. In fact, radio waves are very low energy. This technique works because the nuclei of some molecules absorb radio waves in strong magnetic fields. Radiation is absorbed at characteristic frequencies, making the identification of tiny and impure samples possible. Like infrared, NMR is well used in all chemistry labs. In forensic analysis, it has been used for helping to characterize fake prescription drugs.
Our final technique is mass spectrometry. The first thing to notice is that it is spectroMETRY and not spectroSCOPY. This is not a mistake. Unlike the methods we have learned about so far, mass spectrometry does not involve the absorption of light. Instead, the sample is ionized using high energy electrons. Mass spectrometry, or mass spec, is a hugely important method because it can provide the molecular weight of very complex molecules. But it comes at a cost; this technique destroys the molecule. For this reason, mass spec is normally used after the spectroscopic methods have been completed.
For example, in a hit-and-run accident, a key piece of evidence might be a paint chip left by a fleeing vehicle. Paint has a unique composition, depending on the manufacturer. The tiniest sample can be analyzed first for color and other information by either UV-vis or infrared spectroscopy and then analyzed further using mass spec.
Lesson Summary
In this lesson, you have learned that a number of spectroscopic techniques can be used to analyze unknown materials. Techniques covered in this lesson are ultraviolet-visible spectroscopy, infrared spectroscopy and nuclear magnetic spectroscopy (NMR). These are examples of absorption spectroscopy, which involves the absorption of specific energies of electromagnetic radiation. Absorption 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. These excitations provide us with information about the structure of the molecule.
The absorption wavelength, or frequency, gives the energy associated with a particular excitation. This can be related to a particular part of a molecule. And the absorption intensity provides information on both the ease of transition and the concentration of the absorbing part of the molecule. And, finally, mass spectrometry is a very useful analytical technique that can identify the molecular weight of a molecule. However, it is a destructive technique and should be used after the non-destructive spectroscopic analysis has been completed.
Learning Outcomes
Study this lesson on spectroscopy in pursuit of these goals:
- Understand what spectroscopy entails and its relationship to absorption
- List four spectroscopic techniques and point out the information they can reveal
- Discuss the two types of information provided by an absorption spectra
To unlock this lesson you must be a Study.com Member.
Create your account
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.
|
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.
Infrared spectroscopy is used extensively in chemical and forensic labs. Infrared radiation transfers the right amount of energy to cause vibrational excitation of the bonds in the molecule. Infrared spectroscopy is used for a variety of forensic applications, including analysis of binders and additives in paint and the analysis of alcohol in blood.
Nuclear magnetic resonance (NMR) sounds a lot more sinister than it really is. In fact, radio waves are very low energy. This technique works because the nuclei of some molecules absorb radio waves in strong magnetic fields. Radiation is absorbed at characteristic frequencies, making the identification of tiny and impure samples possible. Like infrared, NMR is well used in all chemistry labs. In forensic analysis, it has been used for helping to characterize fake prescription drugs.
Our final technique is mass spectrometry. The first thing to notice is that it is spectroMETRY and not spectroSCOPY. This is not a mistake. Unlike the methods we have learned about so far, mass spectrometry does not involve the absorption of light. Instead, the sample is ionized using high energy electrons. Mass spectrometry, or mass spec, is a hugely important method because it can provide the molecular weight of very complex molecules. But it comes at a cost; this technique destroys the molecule. For this reason, mass spec is normally used after the spectroscopic methods have been completed.
For example, in a hit-and-run accident, a key piece of evidence might be a paint chip left by a fleeing vehicle. Paint has a unique composition, depending on the manufacturer. The tiniest sample can be analyzed first for color and other information by either UV-vis or infrared spectroscopy and then analyzed further using mass spec.
Lesson Summary
In this lesson, you have learned that a number of spectroscopic techniques can be used to analyze unknown materials. Techniques covered in this lesson are ultraviolet-visible spectroscopy, infrared spectroscopy and nuclear magnetic spectroscopy (NMR). These are examples of absorption spectroscopy, which involves the absorption of specific energies of electromagnetic radiation. Absorption 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. These excitations provide us with information about the structure of the molecule.
The absorption wavelength, or frequency, gives the energy associated with a particular excitation. This can be related to a particular part of a molecule. And the absorption intensity provides information on both the ease of transition and the concentration of the absorbing part of the molecule. And, finally, mass spectrometry is a very useful analytical technique that can identify the molecular weight of a molecule. However, it is a destructive technique and should be used after the non-destructive spectroscopic analysis has been completed.
Learning Outcomes
Study this lesson on spectroscopy in pursuit of these goals:
- Understand what spectroscopy entails and its relationship to absorption
- List four spectroscopic techniques and point out the information they can reveal
- Discuss the two types of information provided by an absorption spectra
To unlock this lesson you must be a Study.com Member.
Create your account
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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BackSpectroscopy Types & Techniques | Absorption, Nuclear Magnetic, & Mass Spectroscopy
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