Infrared (IR) Spectroscopy Principle, Instrumentation, Application

What is Infrared (IR) Spectroscopy?

Infrared (IR) microscopy, also known as vibrational spectroscopy is a method of analysis that takes advantage of the vibrational transitions of a molecule. It is among the most widely employed spectroscopic techniques utilized by organic and inorganic chemical scientists due to its effectiveness in determining the structure of molecules and in identifying them. The technique or method of using infrared spectroscopy involves an instrument known as an infrared-spectrometer (or a spectrophotometer) to create the infrared spectrum.

Principle of Infrared (IR) Spectroscopy

Infrared Spectroscopy is the analysis of infrared light that interacts with molecules. The infrared spectrum that is most suitable to study organic compounds has an infrared wavelength of between 2,500 and 16,000 nm and a frequency range of 1.9*1013 to 1.2*1014 the frequency of which is Hz. The photon energies that are that are associated with this portion of infrared (from 1 to 15 kcal/mole) aren’t enough to trigger electrons, however, they could trigger vibrational excitation of the covalently bonded atoms and groups.

It is well-known that, in addition to the easy rotation of groups around one bond, molecules undergo an array of vibrational motions that are characteristic of their atoms. In turn, all organic compounds absorb infrared radiation , which corresponds in energy to the vibrations. Infrared spectrometers are similar in concept to other spectrometers allow chemists to get absorption spectra for compounds which reflect an exclusive representation of the molecular structures.

The most fundamental measurement made by Infrared spectroscopy is the infrared spectrum. This is a graph of the measured infrared intensities versus the frequency (or frequency) of light. IR Spectroscopy examines the vibratory patterns of atoms and on this , it’s possible to identify which functional groups. The more strong bonds and lighter atoms oscillate at a higher stretch frequency (wavenumber).

Instrumentation of Infrared (IR) Spectroscopy

The principal components of IR the spectrometer are:

• Radiation source
• Sample cells and sampling of substances
• Monochromators
• Detectors
• Recorder

1. IR radiation sources

IR instruments require the use of a source of energy that emits IR radiation that must be constant and intense enough to be detected and extend to what is needed in the wavelength.

The various types of IR radiations are listed below.

• Nernst glower
• Incandescent lamp
• Mercury arc
• Tungsten lamp
• Glober source
• Nichrome wire

2. Sample cells and sampling of substances

IR spectrum has been employed to characterize gas, liquid or solid samples.

• Solid –  A variety of methods are employed for the preparation of solid samples, including the pressed pellet method solid run-in-solution mull technique, solid films and so on.
• Liquid – Liquid samples can be stored in the liquid sample cell that is composed of alkali halides. Solvents that are aqueous cannot be used since they dissolve alkali halids. Only organic solvents, such as chloroform can be utilized.
• Gas– It is similar to the sampling of liquids.

3. Monochromators 

There are many kinds of monochromators: prisms, gratings, and filters. Prisms are constructed of Potassium bromide Sodium chloride, or Caesium Iodide. Filters are comprised of Lithium Fluoride, and Diffraction gratings comprise alkali Halides.

4. Detectors 

Detectors can be used to measure the strength of the infrared radiation. They include thermocouples, Bolometers, thermisters Golay cells, as well as pyroelectric detectors are employed.

In an infrared spectrometer, the detector is a device that measures the intensity of the infrared light that is transmitted or absorbed by the sample.

There are several different types of detectors that are used in IR spectroscopy, including:

1. Thermal detectors: Thermal detectors, also known as bolometers, are devices that measure the change in temperature of a material as a result of absorbed radiation. They are typically used to measure the absorption of infrared light by a sample, and they are sensitive to a wide range of wavelengths.
2. Photovoltaic detectors: Photovoltaic detectors, also known as photodiodes, are devices that convert absorbed radiation into an electrical current. They are typically used to measure the absorption of infrared light by a sample, and they are sensitive to a wide range of wavelengths.
3. Photoconductive detectors: Photoconductive detectors are devices that measure the change in electrical conductivity of a material as a result of absorbed radiation. They are typically used to measure the absorption of infrared light by a sample, and they are sensitive to a wide range of wavelengths.
4. Photoresistive detectors: Photoresistive detectors are devices that measure the change in resistance of a material as a result of absorbed radiation. They are typically used to measure the absorption of infrared light by a sample, and they are sensitive to a wide range of wavelengths.

The specific type of detector used in IR spectroscopy depends on the specific requirements of the measurement, including the sensitivity, wavelength range, and dynamic range of the detector. In general, detectors that are sensitive to a wide range of wavelengths and have a high dynamic range are preferred for IR spectroscopy.

5. Recorders

Recorders are devices used to capture all aspects of the IR spectrum.

In an infrared spectrometer, the detector measures the intensity of the infrared light that is transmitted or absorbed by the sample, and the recorder is a device that records the measurement data.

There are several different types of recorders that are used in IR spectroscopy, including:

1. Strip chart recorders: Strip chart recorders are devices that record data on a continuously moving strip of paper. They are often used to record the absorption spectrum of a sample in real-time, and they are relatively simple and inexpensive.
2. Digital oscilloscopes: Digital oscilloscopes are devices that record and display data in the form of a graph on a computer screen. They are often used to record and analyze the absorption spectrum of a sample in real-time, and they offer a higher resolution and a wider dynamic range than strip chart recorders.
3. Data acquisition systems: Data acquisition systems are devices that collect and store data from multiple sensors or detectors. They are often used to record and analyze the absorption spectrum of a sample in real-time, and they offer a high resolution and a wide dynamic range.

The specific type of recorder used in IR spectroscopy depends on the specific requirements of the measurement, including the resolution, dynamic range, and data storage needs of the recorder. In general, recorders that offer a high resolution and a wide dynamic range are preferred for IR spectroscopy.

Graph of the IR spectrum

Below is a small example of the typical Infrared Absorption Frequency.

So, IR spectroscopy involves the gathering of absorption data and the analysis of that information as an IR spectrum.

Types of Infrared Spectrophotometry

There are several different types of infrared (IR) spectrophotometry that are used to measure the absorption of IR light by molecules. Some common types of IR spectrophotometry include:

1. Fourier transform infrared (FTIR) spectrophotometry

• This is a type of IR spectrophotometry that is based on the Fourier transform, a mathematical technique that allows the spectrum to be analyzed in the frequency domain rather than the time domain.
• FTIR spectrophotometry is widely used due to its high sensitivity and wide dynamic range, and is often used in conjunction with other analytical techniques, such as Raman spectroscopy, to provide a more complete understanding of the sample.

2. Attenuated total reflectance (ATR) spectrophotometry

• This is a type of IR spectrophotometry that is used to analyze solid and liquid samples. It involves placing the sample in contact with a crystal, such as diamond or zinc selenide, and measuring the absorption of IR light as it passes through the crystal.
• ATR spectrophotometry is a non-destructive technique that does not require the sample to be prepared in a specific way, making it suitable for analyzing fragile or valuable samples.

3. Transmission spectrophotometry

• This is a type of IR spectrophotometry that is used to analyze liquid and gas samples. It involves measuring the absorption of IR light as it passes through a cell filled with the sample.
• Transmission spectrophotometry is commonly used to study the structure and composition of gases and liquids.

4. Reflectance spectrophotometry

• This is a type of IR spectrophotometry that is used to analyze solid samples. It involves measuring the reflection of IR light from the surface of the sample.
• Reflectance spectrophotometry is often used to study the surface properties of materials, such as their roughness, smoothness, and chemical composition.

Each type of IR spectrophotometry has its own advantages and disadvantages, and the appropriate technique will depend on the sample and the desired level of sensitivity and resolution.

Comparison between FTIR, ATR, Transmission spectrophotometry, Reflectance spectrophotometry

Fourier transform infrared (FTIR) spectrophotometry, attenuated total reflectance (ATR) spectrophotometry, transmission spectrophotometry, and reflectance spectrophotometry are all types of infrared (IR) spectrophotometry that are used to measure the absorption of IR light by molecules and identify and analyze the functional groups present in a wide range of materials, including polymers, pharmaceuticals, and chemicals. Here is a comparison of these techniques:

• FTIR spectrophotometry: FTIR spectrophotometry is based on the Fourier transform, a mathematical technique that allows the spectrum to be analyzed in the frequency domain rather than the time domain. It is highly sensitive and has a wide dynamic range, and can be used to analyze a wide range of materials, including liquids, gases, solids, and complex mixtures. However, it requires sample preparation for certain types of samples, is limited to certain functional groups, and may be affected by interference from water.
• ATR spectrophotometry: ATR spectrophotometry involves placing the sample in contact with a crystal, such as diamond or zinc selenide, and measuring the absorption of IR light as it passes through the crystal. It is a non-destructive technique that does not require sample preparation, making it suitable for analyzing fragile or valuable samples. However, it is limited to solid and liquid samples and may not be suitable for analyzing gases.
• Transmission spectrophotometry: Transmission spectrophotometry involves measuring the absorption of IR light as it passes through a cell filled with the sample. It is commonly used to study the structure and composition of gases and liquids. However, it requires sample preparation and is limited to liquid and gas samples.
• Reflectance spectrophotometry: Reflectance spectrophotometry involves measuring the reflection of IR light from the surface of the sample. It is often used to study the surface properties of materials, such as their roughness, smoothness, and chemical composition. However, it is limited to solid samples and may not be suitable for analyzing liquids or gases.

Each type of IR spectrophotometry has its own advantages and disadvantages, and the appropriate technique will depend on the sample and the desired level of sensitivity and resolution.

Infrared spectroscopy table

Infrared (IR) spectroscopy is a technique that measures the vibrational, rotational, and other low-frequency modes of molecules in the infrared region of the electromagnetic spectrum. It is a powerful tool for analyzing the molecular structure of a wide range of materials, including polymers, pharmaceuticals, and chemicals.

The IR spectrum of a molecule is a plot of the absorption of infrared light as a function of wavenumber (the reciprocal of the wavelength). Each molecule has a unique set of vibrational modes, and the IR spectrum can be used to identify the specific bonds and functional groups present in the molecule.

An IR spectrum is typically presented as a table or graph, with the wavenumber on the x-axis and the absorption intensity on the y-axis. The absorption intensity is usually expressed as a percentage of the incident light absorbed by the sample.

The IR spectrum is divided into several regions, each corresponding to a different range of wavenumbers:

• The far-infrared region (10-400 cm-1) corresponds to the lowest energy vibrations, such as lattice modes and rotational modes.
• The mid-infrared region (400-4000 cm-1) corresponds to the vibrations of bonds involving C-H, C-C, N-H, O-H, and other common functional groups.
• The near-infrared region (4000-25000 cm-1) corresponds to vibrations of bonds involving C-O, C=O, N-O, and other functional groups.

An IR spectroscopy table typically lists the wavenumber, intensity, and assignment of each absorption band in the IR spectrum. The assignment refers to the specific bond or functional group responsible for the absorption.

For example, an IR spectroscopy table for an ester might include the following entries:

Wavenumber (cm-1)	Intensity	Assignment
2950	strong	C-H stretch
1740	medium	C=O stretch
1460	weak	C-O stretch

This table indicates that the ester has strong absorption at 2950 cm-1 due to C-H stretching, medium absorption at 1740 cm-1 due to C=O stretching, and weak absorption at 1460 cm-1 due to C-O stretching.

Regions of the Infrared spectrum

The infrared (IR) spectrum is the portion of the electromagnetic spectrum that corresponds to wavelengths of light ranging from about 700 nanometers (nm) to 1 millimeter. It is divided into three main regions:

1. Far-infrared (FIR) region: This region corresponds to wavelengths from about 700 nm to 30 micrometers (μm) and is also known as the “thermal infrared” region. It is characterized by low energy vibrations, such as lattice modes and rotational modes, and is often used to study the physical properties of solids and liquids.
2. Mid-infrared (MIR) region: This region corresponds to wavelengths from about 3 μm to 30 μm and is characterized by the vibrations of chemical bonds involving C-H, C-C, N-H, O-H, and other common functional groups. It is often used to identify and analyze the functional groups present in a molecule.
3. Near-infrared (NIR) region: This region corresponds to wavelengths from about 0.7 μm to 3 μm and is characterized by vibrations of bonds involving C-O, C=O, N-O, and other functional groups. It is often used to analyze the composition and structure of materials in the food, pharmaceutical, and chemical industries.

The IR spectrum is typically presented as a plot of the absorption of infrared light as a function of wavenumber (the reciprocal of the wavelength), with the wavenumber on the x-axis and the absorption intensity on the y-axis. Each molecule has a unique set of vibrational modes, and the IR spectrum can be used to identify the specific bonds and functional groups present in the molecule.

Types of Samples used in Infrared Spectroscopy

There are many different types of samples that can be analyzed using infrared (IR) spectroscopy. Some common types of samples include:

1. Liquids: IR spectroscopy can be used to analyze the structure and chemical composition of liquids, such as solvents, acids, and bases.
2. Gases: IR spectroscopy can be used to study the vibrational modes of gases, such as oxygen, nitrogen, and carbon dioxide.
3. Solids: IR spectroscopy can be used to analyze the structure and chemical composition of solids, such as metals, minerals, and polymers.
4. Biological samples: IR spectroscopy can be used to study the structure and function of biological molecules, such as proteins, nucleic acids, and lipids.
5. Complex mixtures: IR spectroscopy can be used to identify and quantify the individual components of complex mixtures, such as fuels, food products, and pharmaceuticals.

There are several different techniques for preparing samples for IR spectroscopy, depending on the type of sample and the desired level of sensitivity. Some common techniques include:

1. KBr pellet method: This method is commonly used for solid samples, and involves grinding the sample with potassium bromide (KBr) and pressing the mixture into a pellet. The pellet is then placed in the IR spectrometer and analyzed.
2. ATR method: This method is used for solid and liquid samples and involves placing the sample in contact with a crystal, such as diamond or zinc selenide, and measuring the absorption of IR light as it passes through the crystal.
3. Transmission method: This method is used for liquid and gas samples and involves measuring the absorption of IR light as it passes through a cell filled with the sample.
4. Reflectance method: This method is used for solid samples and involves measuring the reflection of IR light from the surface of the sample.

What is fourier transform infrared spectroscopy?

• Fourier transform infrared (FTIR) spectroscopy is a type of infrared (IR) spectroscopy that is used to analyze the vibrational, rotational, and other low-frequency modes of molecules. It is a powerful tool for identifying and analyzing the functional groups present in a wide range of materials, including polymers, pharmaceuticals, and chemicals.
• FTIR spectroscopy works by measuring the absorption of IR light as a function of wavenumber (the reciprocal of the wavelength). The sample is placed in the path of an IR beam, and the absorption of the IR light is measured as a function of wavenumber. The resulting spectrum is a plot of the absorption intensity as a function of wavenumber, and can be used to identify the specific bonds and functional groups present in the sample.
• FTIR spectroscopy is based on the Fourier transform, which is a mathematical technique that allows the spectrum to be analyzed in the frequency domain rather than the time domain. This makes it possible to measure the spectrum over a wide range of wavenumbers in a single scan, and allows for more precise and accurate analysis of the sample.
• FTIR spectroscopy is widely used in a variety of fields, including chemistry, biology, material science, and environmental science, and is often used in conjunction with other analytical techniques, such as Raman spectroscopy, to provide a more complete understanding of the sample.

What is near infrared spectroscopy?

Near infrared (NIR) spectroscopy is a type of infrared (IR) spectroscopy that is used to analyze the vibrational modes of molecules in the near-infrared region of the electromagnetic spectrum (wavelengths ranging from about 0.7 micrometers to 3 micrometers). It is a powerful tool for identifying and analyzing the functional groups present in a wide range of materials, including polymers, pharmaceuticals, and chemicals.

NIR spectroscopy works by measuring the absorption of NIR light as a function of wavenumber (the reciprocal of the wavelength). The sample is placed in the path of an NIR beam, and the absorption of the NIR light is measured as a function of wavenumber. The resulting spectrum is a plot of the absorption intensity as a function of wavenumber, and can be used to identify the specific bonds and functional groups present in the sample.

NIR spectra are typically characterized by the vibrations of bonds involving C-O, C=O, N-O, and other functional groups. The NIR region is particularly useful for analyzing the structure and composition of materials in the food, pharmaceutical, and chemical industries, as many functional groups absorb NIR light strongly.

NIR spectroscopy is widely used in a variety of fields, and is often used in conjunction with other analytical techniques, such as Raman spectroscopy, to provide a more complete understanding of the sample. It is a non-destructive technique, meaning that the sample is not altered during analysis, making it suitable for analyzing fragile or valuable samples.

Why do Molecules Only Absorb IR Frequency Resonant to Their Internal Vibrational Frequencies?

Molecules only absorb infrared (IR) frequencies that are resonant with their internal vibrational frequencies because the energy of the absorbed IR light must be equal to the energy difference between two vibrational energy levels of the molecule. This is known as the selection rule for vibrational transitions.

When a molecule absorbs an IR photon, it absorbs energy that is equal to the energy difference between two vibrational energy levels. The vibrational energy levels of a molecule are determined by the bond lengths, bond angles, and other structural parameters of the molecule. Each vibrational mode corresponds to a specific vibrational energy level, and the energy difference between two vibrational energy levels is equal to the energy of the absorbed IR photon.

Therefore, a molecule will only absorb an IR photon if the energy of the IR photon is equal to the energy difference between two vibrational energy levels of the molecule. This means that the IR frequency must be resonant with the internal vibrational frequencies of the molecule.

For example, if the vibrational energy levels of a molecule are separated by an energy of 1000 cm-1, then the molecule will only absorb IR photons with a frequency of 1000 cm-1. This frequency will be absorbed by the molecule, while other frequencies will not be absorbed.

This is why molecules only absorb IR frequencies that are resonant with their internal vibrational frequencies. It is also why the IR spectrum of a molecule is a fingerprint of its vibrational modes and can be used to identify the specific bonds and functional groups present in the molecule.

Types of vibrations

The type of vibrations or vibrational modes refers to the positional variations of the atoms constituting the link. Stretching and bending are the two primary types of vibrational modes.

1. Stretching

This entails modifications to the bond length between atoms. Either the atoms can move closer together, so lengthening the connection, or farther apart, thereby weakening it.

Stretching can be categorised as;

• Symmetric stretching: When two atoms simultaneously move toward or away from a centre atom, this is symmetric stretching.
• Asymmetric stretching: Asymmetric stretching occurs when two atoms attached to a core atom move in opposite directions.

2. Bending

This sort of vibration refers to changes in the ‘angle’ between two bonds and is subdivided as follows:

• Rocking: when two atoms move in opposite directions on the same plane.
• Scissoring: When two atoms move towards or away from one another in the same plane, they are scissoring.
• Twisting: Twisting occurs when two atoms travel out of the plane in opposite directions.
• Wagging: an out-of-plane vibration in which the atoms simultaneously move away from and toward one another in a v-shape.

What are the units of spectroscopy?

Spectroscopy is the study of the interaction of electromagnetic radiation with matter. In spectroscopy, the intensity or intensity ratio of the radiation is typically measured as a function of wavelength, frequency, or energy. The units used to express these measurements depend on the specific type of spectroscopy being used and the nature of the radiation being measured.

In many cases, spectroscopy measurements are expressed in terms of the energy or frequency of the radiation. The energy of electromagnetic radiation is typically expressed in units of electron volts (eV), while the frequency is typically expressed in units of Hertz (Hz).

In other cases, spectroscopy measurements are expressed in terms of the wavelength of the radiation. The wavelength is the distance between two adjacent peaks or troughs of a wave, and it is typically expressed in units of meters (m), nanometers (nm), or angstroms (Å).

In infrared (IR) spectroscopy, the absorption or transmittance of infrared light is often expressed in units of absorbance (A) or transmittance (%T). Absorbance is defined as the logarithm of the ratio of the intensity of the incident light to the intensity of the absorbed light, and it is typically expressed on a scale from 0 to 10. Transmittance is defined as the ratio of the intensity of the transmitted light to the intensity of the incident light, and it is typically expressed as a percentage.

In ultraviolet-visible (UV-Vis) spectroscopy, the absorption or transmittance of ultraviolet or visible light is often expressed in units of absorbance or transmittance, as in IR spectroscopy. In addition, the absorption or transmittance may also be expressed in terms of the molar absorbance coefficient (ε) or the molar extinction coefficient (ε), which are related to the concentration and molar mass of the sample.

In nuclear magnetic resonance (NMR) spectroscopy, the intensity of the magnetic resonance signal is typically expressed in units of parts per million (ppm). The chemical shift of the signal is often expressed in units of ppm relative to a reference compound.

In mass spectrometry, the intensity of the ionized species is typically expressed in units of counts per second (cps) or relative abundance. The mass-to-charge ratio (m/z) of the ions is often expressed in units of atomic mass units (amu).

Infrared vs Raman spectroscopy

Infrared (IR) spectroscopy and Raman spectroscopy are two techniques that are used to identify and analyze the molecular structure of a substance. Both techniques involve the interaction of light with a sample, but they differ in the way that the light is used to probe the sample.

Infrared spectroscopy involves the absorption of infrared light by a sample. Infrared light has a longer wavelength than visible light, and it is absorbed by certain vibrational modes of the bonds between atoms in a molecule. By measuring the absorption of infrared light at different wavelengths, it is possible to determine the vibrational modes of the bonds in the molecule, which can be used to identify the molecular structure of the sample.

Raman spectroscopy, on the other hand, involves the scattering of light by a sample. When light is scattered by a sample, some of the scattered light is shifted to a higher or lower energy level. This energy shift is called the Raman shift, and it is caused by the vibrational and rotational modes of the bonds in the molecule. By measuring the Raman shift of the scattered light at different wavelengths, it is possible to determine the vibrational and rotational modes of the bonds in the molecule, which can also be used to identify the molecular structure of the sample.

Both IR and Raman spectroscopy are widely used in a variety of fields, including chemistry, materials science, and biology. They are powerful tools for identifying and analyzing the molecular structure of a wide range of materials, including organic and inorganic compounds, polymers, and biomolecules.

What is necessary condition for IR spectroscopy?

There are several conditions that are necessary for infrared (IR) spectroscopy to be successful. These include:

1. The presence of bonds that absorb infrared light: IR spectroscopy relies on the absorption of infrared light by certain vibrational modes of the bonds between atoms in a molecule. In order for IR spectroscopy to be useful, the sample must contain bonds that absorb infrared light.
2. A transparent or translucent sample: IR spectroscopy involves the measurement of the absorption of infrared light by a sample. In order for the measurement to be accurate, the sample must be transparent or translucent, so that the infrared light can pass through it.
3. A stable sample: IR spectroscopy involves the measurement of the absorption of infrared light by a sample over a certain period of time. In order for the measurement to be accurate, the sample must be stable and not undergo any changes during the measurement.
4. A representative sample: In order for IR spectroscopy to be useful, the sample must be representative of the material being analyzed. This means that the sample must be representative of the average molecular structure of the material, and it must not be contaminated with any other materials.
5. A suitable solvent: In many cases, it is necessary to dissolve the sample in a solvent in order to prepare it for IR spectroscopy. The choice of solvent can affect the absorption spectrum of the sample, and it is important to choose a solvent that does not interfere with the measurement of the absorption of the sample.
6. Suitable instrumentation: IR spectroscopy requires specialized instrumentation, such as an infrared spectrometer, to measure the absorption of infrared light by the sample. The sensitivity and resolution of the instrumentation can affect the accuracy and precision of the measurement.

Applications of Infrared (IR) Spectroscopy

It has been of major importance to scientists in diverse fields like:

• Protein characterization
• Nanoscale analysis of semiconductors as well as
• Space exploration.
• Analyzing gaseous, liquid or solid samples
• Identification of compounds
• Quantitative analysis
• Information on the functional groups of molecules as well as the structure of molecules could be derived by IR spectrum
• To learn about interactions between molecules

Infrared Spectrophotometry Advantages

• Non-destructive: IR spectrophotometry is a non-destructive technique, meaning that the sample is not altered during analysis. This makes it suitable for analyzing fragile or valuable samples.
• High sensitivity: IR spectrophotometry is highly sensitive and can detect trace amounts of certain functional groups.
• Wide range of applications: IR spectrophotometry has a wide range of applications and can be used to analyze a variety of materials, including liquids, gases, solids, and complex mixtures.
• Versatility: IR spectrophotometry can be used in conjunction with other analytical techniques, such as Raman spectroscopy, to provide a more complete understanding of the sample.
• You can receive both qualitative (structure, presence of functional groups) and quantitative (number of chemicals in the sample) information.
• Different IR regions can be optimised for particular applications, such as the far IR region for the study of inorganic chemicals, the mid-IR region for organic species, and the near IR region for routine quantitative analysis.
• Data interpretation of the regularly employed mid-IF area is straightforward; peak intensities, peak positions, peak widths, and peak shapes can be read readily, and data may be extracted rapidly.
• The FTIR spectrometer can acquire data quickly and with a higher signal-to-noise ratio.

Infrared Spectrophotometry Disadvantages

• Requires sample preparation: Some types of IR spectrophotometry, such as transmission spectrophotometry, require the sample to be prepared in a specific way (e.g., placed in a cell). This can be time-consuming and may require specialized equipment.
• Limited to certain functional groups: IR spectrophotometry is limited to the vibrational modes of certain functional groups, and may not be suitable for analyzing all types of molecules.
• Interference from water: Water absorbs IR light strongly and can interfere with the analysis of certain samples. This can be mitigated by using a technique such as attenuated total reflectance (ATR) spectrophotometry, which does not require the sample to be prepared in a specific way.
• Limited to certain sample types: Some types of IR spectrophotometry, such as reflectance spectrophotometry, are limited to solid samples and may not be suitable for analyzing liquids or gases.
• IR spectrophotometry provides no information regarding molecular mass or the relative positions of functional groups.
• A single IR absorption spectra cannot determine if an unidentified material is pure or a combination of components.
• Materials that absorb IR, such as plastic and glass, cannot be utilised in an IR spectrophotometer.
• The dispersive spectrophotometer has low sensitivity and is relatively sluggish.

FAQ

References

• Kamariotis, A.; Boyarkin, O. V.; Mercier, S. R.; Beck, R. D.; Bush, M. F.; Williams, E. R.; Rizzo, T. R. J. Am. Chem. Soc. 2006, 128, 905
• Peter J. Larkin. “Infrared and Raman Spectroscopy. Principles and Spectral Interpretation” Chapters 1 to 6. Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands. Elsevier 2011
• Marwa El-Azazy. Introductory Chapter: Infrared Spectroscopy – A Synopsis of the Fundamentals and Applications, Infrared Spectroscopy – Principles, Advances, and Applications. 2018. IntechOpen, DOI: 10.5772/intechopen.82210
• Donald L. Pavia, Gary M. Lampman and George S. Kriz. “Introduction to Spectroscopy. A Guide for Students of Organic Chemistry” Chapter 2. Thompson Learning. United States of America 2001.