Types of Spectroscopy with Definition, Principle, Steps, Uses

What is spectroscopy?

• Spectroscopy is an analytical technique that delves into how light interacts with matter, focusing on the absorption, emission, and dispersion of electromagnetic radiation by substances under scrutiny. This field is pivotal in unraveling the characteristics of materials at the molecular and atomic levels, including their composition, physical structure, and electronic configurations.
• A fundamental tool in spectroscopy is the spectrometer, a versatile instrument designed to gauge the variations in physical properties induced by a sample across a specified range. The functionality of spectrometers varies with their type; for instance, NMR spectrometers assess changes in nuclear resonance frequencies, mass spectrometers examine variations in mass-to-charge ratios, and optical spectrometers analyze alterations in electromagnetic radiation.
• A specialized form of the spectrometer is the spectrophotometer, which specifically measures how a sample interacts with electromagnetic radiation, including absorption, reflection, and scattering, as well as the emission phenomena like fluorescence and phosphorescence. Commonly employed in laboratory settings, spectrophotometers facilitate the quantification of sample concentrations by evaluating the total light absorbed by the sample.
• Another key instrument in the spectroscopic arsenal is the spectroscope, or optical spectrometer, which quantifies various light properties over a designated spectral range, primarily focusing on light intensity and, in certain cases, polarization. Historically, spectroscopes utilized prisms, but modern devices often incorporate diffraction gratings, adjustable slits, and photodetectors. These instruments are indispensable in chemistry and astronomy for deducing the chemical compositions of various samples based on the radiation they emit.
• The spectrograph, closely related to the spectroscope, is adept at detecting light and segregating it by wavelength or frequency, which are then captured by multiple detectors. Predominantly used in astronomy, spectrographs attached to telescopes collect light from celestial bodies, which is then dispersed by a diffraction grating to analyze the chemical constituents of these astronomical entities.
• In the broader context, the term “spectra” refers to the array of colors manifested when white light is dispersed through a prism, encompassing a wide range of variables related to light and other waveforms. The electromagnetic spectrum, for example, is a critical concept in spectroscopy, representing the range of electromagnetic radiation frequencies that characterize the distribution of radiation absorbed or emitted by an object. Additionally, spectroscopy also encompasses the mass spectrum, which relates ion abundance to mass-to-charge ratios, and the electron spectrum, which involves the distribution of particle beams based on particle energy.

Types of Spectroscopy

Spectroscopy encompasses a broad range of techniques based on the interaction between light and matter, each with its own unique applications and principles. Here’s an overview of some key types:

1. Absorption Spectroscopy: This method measures the wavelengths of light absorbed by a sample, revealing its composition based on the principle that each material has a unique absorption spectrum. It’s widely used in chemical analysis and environmental monitoring.
2. Astronomical Spectroscopy: Utilizing the electromagnetic spectrum emitted by celestial bodies, this form of spectroscopy provides insights into the composition, temperature, and movement of stars and galaxies.
3. Atomic Absorption Spectroscopy (AAS): AAS is particularly effective for analyzing metal elements in samples by measuring the absorption of light by free atoms in the gas phase.
4. Circular Dichroism (CD) Spectroscopy: CD measures the differential absorption of left and right circularly polarized light, providing information about the secondary structure of chiral molecules, such as proteins.
5. Electrochemical Impedance Spectroscopy (EIS): This technique measures the impedance of a system to an applied AC voltage, useful in studying battery technologies and corrosion.
6. Electron Spin Resonance (ESR) Spectroscopy: ESR detects species with unpaired electrons by measuring their transitions between magnetic energy levels, applicable in studying free radicals and transition metal complexes.
7. Emission Spectroscopy: This technique involves analyzing light emitted by a substance when it’s excited, commonly used for elemental analysis.
8. Energy Dispersive Spectroscopy (EDS): Often paired with electron microscopy, EDS characterizes elemental composition by detecting X-rays emitted from a sample.
9. Fluorescence Spectroscopy: This method examines the fluorescence emitted by certain substances, providing insights into the structure and dynamics of complex molecules.
10. Fourier-Transform Infrared (FTIR) Spectroscopy: FTIR identifies chemical bonds in a molecule by producing an infrared absorption spectrum, useful in analyzing organic compounds.
11. Gamma-ray Spectroscopy: Applied mainly in nuclear physics, this technique studies the gamma rays emitted by radioactive substances, offering insights into nuclear structures and processes.
12. Infrared (IR) Spectroscopy: IR spectroscopy identifies molecular vibrations, giving detailed information about molecular structure, especially functional groups in organic compounds.
13. Magnetic Resonance Spectroscopy (MRS): MRS provides a non-invasive way to study metabolic changes in brain and body tissues, complementing MRI in medical diagnostics.
14. Mass Spectroscopy (MS): MS analyzes the mass-to-charge ratio of ions to identify and quantify molecules in a sample, widely used in chemistry and biochemistry.
15. Molecular Spectroscopy: This broad category includes techniques that probe the interactions between electromagnetic radiation and molecules, revealing structural information.
16. Mossbauer Spectroscopy: Utilizing the recoil-free emission and absorption of gamma rays by atomic nuclei, this method can elucidate fine details of atomic and magnetic structures.
17. Nuclear Magnetic Resonance (NMR) Spectroscopy: NMR explores the magnetic properties of atomic nuclei, providing detailed information about molecular structure and dynamics.
18. Photoelectron Spectroscopy: This technique measures the kinetic energy of electrons ejected from materials upon exposure to light, aiding in surface analysis and chemical state determination.
19. Raman Spectroscopy: Raman analyzes vibrational, rotational, and other low-frequency modes in a system, offering insights into molecular vibrations and chemical composition.
20. UV Spectroscopy: UV spectroscopy studies the absorption of ultraviolet light, which can induce electronic transitions in molecules, commonly used in analytical chemistry.
21. UV/Vis Spectroscopy: This method extends into the visible spectrum, allowing for a broader range of compound analyses, including concentration determination and chemical kinetics.
22. X-ray Photoelectron Spectroscopy (XPS): XPS investigates the surface composition and electronic structure of materials by measuring the kinetic energy of electrons emitted from a sample exposed to X-rays.

Each spectroscopic method brings unique insights into the physical, chemical, and structural properties of materials, finding applications across science, from chemical and biological research to materials science and astrophysics.

Technique	Principle	Applications
Absorption Spectroscopy	Measures light absorption to determine material composition	Chemical analysis, environmental monitoring
Astronomical Spectroscopy	Analyzes electromagnetic spectrum from celestial bodies	Studying stars, galaxies, and universe composition
Atomic Absorption Spectroscopy (AAS)	Measures light absorption by free gas-phase atoms	Metal analysis in various samples
Circular Dichroism (CD) Spectroscopy	Differential absorption of circularly polarized light	Studying chiral molecules, protein secondary structures
Electrochemical Impedance Spectroscopy (EIS)	Measures system impedance to AC voltage	Battery research, corrosion studies
Electron Spin Resonance (ESR) Spectroscopy	Detects transitions between magnetic energy levels of unpaired electrons	Free radical and transition metal complex studies
Emission Spectroscopy	Analyzes light emitted by excited substances	Elemental analysis, industrial applications
Energy Dispersive Spectroscopy (EDS)	Detects X-rays emitted from a sample	Elemental analysis, used with electron microscopy
Fluorescence Spectroscopy	Examines fluorescence emitted by substances	Molecular structure and dynamics studies
Fourier-Transform Infrared (FTIR) Spectroscopy	Produces an infrared absorption spectrum to identify chemical bonds	Organic compound analysis
Gamma-ray Spectroscopy	Studies gamma rays from radioactive decay	Nuclear structure and processes, astronomical research
Infrared (IR) Spectroscopy	Identifies molecular vibrations for structural information	Analysis of functional groups in organic compounds
Magnetic Resonance Spectroscopy (MRS)	Studies metabolic changes in tissues using magnetic resonance	Complements MRI in medical diagnostics
Mass Spectroscopy (MS)	Analyzes mass-to-charge ratio of ions	Identification and quantification of molecules
Molecular Spectroscopy	Interactions between electromagnetic radiation and molecules	Structural analysis of compounds
Mossbauer Spectroscopy	Recoil-free emission and absorption of gamma rays by nuclei	Atomic and magnetic structure analysis
Nuclear Magnetic Resonance (NMR) Spectroscopy	Explores magnetic properties of atomic nuclei	Molecular structure and dynamics determination
Photoelectron Spectroscopy	Measures kinetic energy of electrons ejected by light	Surface analysis, chemical state determination
Raman Spectroscopy	Analyzes vibrational, rotational, and other low-frequency modes	Molecular vibrations and chemical composition analysis
UV Spectroscopy	Studies ultraviolet light absorption inducing electronic transitions	Analytical chemistry applications
UV/Vis Spectroscopy	Extends into the visible spectrum for broader compound analysis	Concentration determination, chemical kinetics
X-ray Photoelectron Spectroscopy (XPS)	Investigates surface composition and electronic structure	Surface analysis, material science

1. Atomic absorption spectroscopy

• Atomic absorption spectroscopy (AAS) is a precise analytical method based on the principles of spectroscopy, designed for the quantitative determination of specific chemical elements within a sample. This technique hinges on a fundamental interaction between light and atoms, offering a detailed insight into the composition of various substances.
• The core process of AAS involves the generation of free electrons within an atomizer, a device that converts the sample into a gaseous state where atoms are in their elemental form. When these free electrons are exposed to ultraviolet (UV) or visible light, they absorb specific wavelengths of this radiation, leading to an elevation in their energy levels. This transition of electrons to higher energy orbits is a key event in AAS.
• As the electrons absorb energy, an absorption spectrum is created. This spectrum is a unique fingerprint for each element, as every type of atom has a distinct pattern of energy absorption due to its unique electronic structure. Photodetectors within the spectrometer are tasked with capturing this spectrum, converting the absorbed light into measurable signals.
• The intensity of the absorption spectrum is directly related to the number of atoms in the gaseous state and, consequently, the concentration of the specific element in the sample. The principle behind this is known as Beer’s law, which posits that the absorbance of light by a sample is directly proportional to the concentration of absorbing molecules present. Therefore, by measuring the absorbance, AAS provides a means to quantify the amount of a particular element within the sample.
• This method is widely employed in various fields, such as environmental monitoring, pharmacology, and the analysis of metals in food and water, due to its specificity, sensitivity, and ability to provide rapid and accurate measurements of elemental concentrations.

The steps of Atomic absorption spectroscopy

1. Sample Preparation: The first step in AAS is preparing the sample for analysis. This typically involves taking a liquid sample and mixing it with a solvent, often a spirit, to ensure it is in a suitable form for vaporization. The solution is placed into a container or flask designed for the AAS instrument.
2. Vaporization: The liquid sample, now mixed with the solvent, is introduced into an atomizer. Here, it is vaporized into a gaseous state using a heat source, commonly a fuel-rich flame, such as acetylene-nitrous oxide. This process effectively breaks the sample down into free atoms in a gaseous state, a crucial step for atomic absorption measurement.
3. Light Source Activation: A lamp emitting light at specific wavelengths is used as the light source. This wavelength is carefully chosen to match the absorption spectrum of the element being analyzed. When the light passes through the vaporized sample, atoms of the target element absorb light at this specific wavelength.
4. Detection: As the gaseous atoms absorb the light, their concentration is measured by a detector that records the absorbance level. The absorbance is indicative of how much light has been absorbed by the atoms in the gas, correlating directly with the concentration of the element in the sample.
5. Baseline Correction: To ensure accuracy, the instrument also measures the absorbance of a solvent blank, which contains all the components of the sample except for the analyte (the element being measured). This step helps in correcting for any absorbance that might be caused by the solvent or other components in the sample.
6. Standard Calibration: A standard solution containing a known concentration of the analyte is analyzed using the same process. This step is critical for calibrating the instrument and establishing a relationship between absorbance and concentration.
7. Quantification: Finally, a graph is plotted with absorbance on the y-axis and concentration on the x-axis, using the data from the standard solutions. The absorbance measured for the sample can then be compared to this calibration curve to determine the concentration of the element within the sample.

Applications of Atomic absorption spectroscopy

• Analysis in Biological Systems: AAS is instrumental in studying biological samples, such as tissues, blood, and other bodily fluids, to detect and quantify the presence of essential and trace metals. This capability is crucial for understanding physiological processes, diagnosing deficiencies or toxicities, and researching the role of metals in biological systems.
• Detection of Metal Impurities: The technique is highly valued in the metallurgical industry for its ability to detect and measure trace amounts of metals in alloys and other mixtures. This is essential for quality control and ensuring that products meet specified standards regarding their composition.
• Environmental Monitoring: AAS plays a significant role in environmental science, particularly in the analysis of water and soil samples. It is used to monitor pollution levels, detect the presence of heavy metals, and assess the quality of natural resources, contributing to environmental protection and regulatory compliance.
• Pharmaceutical Analysis: In the pharmaceutical industry, AAS is employed to ensure the purity of products by detecting trace metals that might be present as contaminants. This is vital for maintaining the safety and efficacy of pharmaceuticals.
• Analysis of Oil Products: The technique is also applied in the petrochemical industry to analyze metal content in oil products. Metals can be present due to the oil’s origin or as a result of contamination during processing. Monitoring these levels is important for both product quality and the maintenance of processing equipment.

2. Absorption spectroscopy

• Absorption spectroscopy is an analytical method used to identify and quantify substances through the absorption of electromagnetic radiation at specific wavelengths. This technique is predicated on the principle that every substance can absorb radiation to a certain degree, which is determined by its unique molecular structure.
• In essence, absorption spectroscopy involves shining a beam of light through a sample and measuring how much of the light is absorbed by the sample. The absorbed light corresponds to certain energy levels where electrons within the molecules of the sample transition from a lower energy state to a higher one. The pattern of absorption across various wavelengths is known as an absorption spectrum, which can serve as a “fingerprint” for identifying substances.
• The process starts by directing a beam of light, which can range from ultraviolet to visible or infrared, at a sample. As the light passes through, some of it is absorbed, while the rest is transmitted. The degree of light absorption is measured by a detector, and the data obtained is used to create an absorption spectrum. This spectrum displays the absorbance levels across different wavelengths, showcasing where the sample has absorbed the light.
• This technique is extensively used in various scientific fields for both qualitative and quantitative analysis. It helps in determining the presence of specific substances within a mixture and quantifying their concentration. Additionally, absorption spectroscopy is instrumental in studying the molecular structure and dynamics of substances, making it invaluable in research areas such as chemistry, physics, biology, and environmental science.
• The simplicity, efficiency, and non-destructive nature of absorption spectroscopy make it a preferred method for analyzing samples in laboratories. With its ability to provide detailed information about the composition and characteristics of substances, absorption spectroscopy continues to be a cornerstone analytical technique in scientific investigations.

Working Principle of Absorption spectroscopy

• The foundational principle of absorption spectroscopy lies in the unique interaction between electromagnetic radiation and matter. This interaction is governed by the material’s atomic and molecular structure, which determines its capacity to absorb radiation at various frequencies. The essence of absorption spectroscopy is to explore and measure this capacity, revealing insights into the substance’s composition and concentration.
• At the heart of this technique is the concept of the absorption spectrum, which is essentially a profile detailing the range and intensity of radiation absorbed by a material across different frequencies. This spectrum is influenced by the inherent properties of the atoms and molecules that constitute the material. Specifically, each type of atom or molecule has distinct energy states, and transitions between these states can absorb radiation of particular frequencies.
• When a photon, or a particle of light, encounters a material, it can impart its energy to the material’s electrons, causing them to transition to higher energy states. This process is contingent on the photon’s energy aligning with the energy gap between the electron’s current and potential higher energy state. The resulting absorption of photons at specific energies leads to the formation of what are known as absorption lines. Collectively, these lines compose the absorption spectrum of the material.
• The intensity of absorption, quantified as absorbance, is directly related to the number of electrons that undergo such transitions. Consequently, the absorbance can provide quantitative information about the material. Specifically, the greater the number of molecules capable of absorbing photons at a given frequency, the higher the absorbance at that frequency. This relationship enables the determination of the concentration of absorbing molecules within the sample.
• In summary, absorption spectroscopy capitalizes on the fundamental principle that materials absorb electromagnetic radiation in a manner that is highly specific to their atomic and molecular composition. By analyzing the absorption spectrum, scientists can deduce valuable information about the material’s characteristics, including its composition and the concentration of its constituents. This principle makes absorption spectroscopy a powerful tool in a wide array of scientific and industrial applications, from chemical analysis to quality control and beyond.

The steps of absorption

1. Preparation of Cuvettes: Initially, two cuvettes are prepared, one for the solvent and the other for the sample solution. Cuvettes are transparent containers designed specifically for spectroscopic experiments, allowing light to pass through the solution they contain.
2. Baseline Measurement with Solvent: The cuvette containing the solvent is placed into the spectrometer first. This step is crucial for establishing a baseline measurement, as it accounts for any potential light loss attributable to scattering and absorption by the solvent itself. This baseline is necessary to ensure that subsequent measurements of the sample accurately reflect only the absorption attributable to the sample and not the solvent.
3. Measurement of Sample Solution: Following the baseline assessment, the cuvette filled with the sample solution is placed into the spectrometer. The device then measures the light absorbed by the sample across a range of wavelengths, typically between 200 and 800 nanometers, which encompasses the ultraviolet to visible light spectrum.
4. Recording Absorbance Data: As the spectrometer scans through the different frequencies of light, it records the absorbance levels exhibited by the sample. Absorbance is indicative of how much light the sample absorbs at each wavelength, with higher absorbance values signifying greater absorption.
5. Creating a Spectrum: The collected data from the sample’s exposure to various light frequencies is used to construct an absorbance spectrum. This spectrum represents a graphical depiction of the absorbance values across the scanned wavelength range, providing insights into the sample’s absorption characteristics.
6. Concentration Analysis: To quantify the concentration of substances within the sample, the absorbance values are plotted against the known concentrations of similar samples. This calibration curve enables the determination of the unknown concentration in the sample by comparing its absorbance to that of standards with known concentrations.

Applications

• Identification of Substances:
  • Determines the presence of specific compounds within a sample by analyzing the unique absorption patterns.
  • Helps in characterizing unknown substances by comparing their absorption spectra with known standards.
• Quantitative Analysis:
  • Quantifies the concentration of substances in a sample by measuring the absorbance levels at specific wavelengths.
  • Utilized in chemistry labs for precise measurements of solute concentrations in solutions.
• Remote Sensing:
  • Employs absorption spectroscopy for monitoring environmental pollutants and hazardous substances from a distance.
  • Facilitates the analysis of atmospheric gases, water pollutants, and soil contaminants without physical sample collection.
• Structural Analysis:
  • Assists in understanding the molecular and atomic structure of substances.
  • Provides insights into the electronic transitions and energy states of molecules, aiding in the study of chemical bonds and reactions.
• Environmental Monitoring:
  • Tracks changes in environmental conditions by detecting and quantifying pollutants in air, water, and soil.
  • Essential for assessing the impact of industrial activities on natural resources and public health.
• Pharmaceutical Applications:
  • Used in drug testing and development to determine the purity and composition of pharmaceutical compounds.
  • Helps in ensuring the safety and efficacy of medications through rigorous quality control.
• Food Industry:
  • Analyzes food products for the presence of additives, contaminants, and nutrient levels.
  • Supports the enforcement of food safety standards and nutritional labeling.
• Research and Development:
  • Facilitates the exploration of new materials and compounds in research labs.
  • Contributes to advancements in fields such as nanotechnology, materials science, and biochemistry.

3. Astronomical spectroscopy

• Astronomical spectroscopy involves analyzing the light spectrum emitted or reflected by celestial bodies such as stars, planets, and galaxies. This scientific method relies on spectroscopy principles to dissect the electromagnetic spectrum emanating from these objects. The core of this study hinges on understanding that the spectrum obtained from celestial light sources exhibits unique characteristics, differing significantly from a simple white light spectrum.
• When celestial light is dissected using a diffraction grating, it reveals a series of absorption and emission lines. These lines are critical for scientists as they provide insights into the physical properties of the source. They are formed due to the interaction of light with the electrons in atoms and molecules, which absorb or emit light at specific wavelengths depending on their energy levels.
• The resulting spectrum, showcasing these absorption and emission lines, is then analyzed. Scientists plot the observed wavelengths against the intensity of light (flux) at each point to study these features in detail. Notably, many of these spectral lines are attributed to the presence of various metals within the celestial object. By examining the characteristics of these lines, such as their width and intensity, astronomers can infer the composition and abundance of elements within the object being studied.
• Astronomical spectroscopy serves as a fundamental tool in astrophysics, enabling researchers to glean detailed information about the chemical composition, temperature, density, and even the motion of celestial bodies, thereby enhancing our understanding of the universe’s complexities.

Steps of Astronomical spectroscopy

1. Collection of Light: The initial step involves capturing the incoming light from a celestial object. This is typically done using a telescope, which gathers the light and directs it towards the spectroscope. Telescopes act as the primary tool for collecting as much light as possible from distant stars or other astronomical objects.
2. Dispersion of Light: Once the light enters the spectroscope, it encounters a diffraction grating. This component is crucial for separating the light into its constituent wavelengths. The diffraction grating works by bending the light at different angles depending on its wavelength, effectively spreading the light into a spectrum.
3. Detection and Analysis: The spread-out wavelengths of light then strike photodetectors. These detectors are sensitive to various wavelengths and can measure the intensity of the light across the spectrum. The data collected by the photodetectors is used to construct a detailed spectrum, showing how the intensity of the light varies with wavelength.
4. Flux Calibration: To make sense of the raw data, the spectrum’s flux scale must be calibrated. This involves comparing the observed spectrum with that of standard stars, whose properties are well understood. By doing so, astronomers can correct for any distortions or biases introduced by the atmosphere, the telescope, or the spectroscope itself, ensuring that the final spectrum accurately reflects the true nature of the light from the celestial object.

Applications of Astronomical spectroscopy

• Determining Chemical Composition: One of the most fundamental applications of spectroscopy is to ascertain the chemical makeup of stars and other celestial objects. By examining the absorption lines in the spectrum of a star, scientists can identify the presence of various elements and compounds, revealing the star’s composition.
• Measuring Temperature: The characteristics of spectral lines, including their width and intensity, also provide clues about the temperature of a celestial body. For instance, the spectrum of a hot star will show lines corresponding to higher energy transitions, while a cooler star will exhibit lines indicative of lower energy transitions.
• Assessing Density and Mass: The density and mass of stars and other astronomical objects can be inferred from their spectra. Certain spectral lines are sensitive to the density of the emitting or absorbing material, allowing astronomers to estimate these physical properties.
• Studying Relative Motion: Spectroscopy is invaluable for understanding the motion of stars and galaxies. The Doppler effect, which causes the wavelength of light to shift depending on the relative motion of the source and the observer, can be observed in the spectra of celestial objects. This shift, known as redshift when the object is moving away and blueshift when it is approaching, provides critical information about the speed and direction of movement.
• Exploring Galaxy Composition and Structure: Beyond individual stars, spectroscopy is essential for studying entire galaxies. By analyzing the collective light from all the stars within a galaxy, astronomers can gain insights into the galaxy’s overall composition and the distribution of its constituent stars and gas.
• Investigating Stellar and Galactic Evolution: The information gleaned from spectroscopic studies also contributes to our understanding of how stars and galaxies form, evolve, and eventually meet their end. The abundance of certain elements, for example, can indicate a star’s age and its stage in the stellar lifecycle.

4. UV spectroscopy

• UV spectroscopy, or ultraviolet-visible spectroscopy, is an analytical technique that utilizes the absorption of UV light by electrons to provide information about the composition and concentration of substances. Here’s an overview of its principle, steps, and applications:
• Principle of UV Spectroscopy:
  • Electron Excitation: UV spectroscopy involves the absorption of UV radiation by electrons in a sample.
  • Energy State Transition: When UV light is absorbed, electrons transition from lower to higher energy states.
  • Absorption Spectrum Formation: This excitation generates an absorption spectrum, where the amount of absorbed radiation is measured as absorbance.
  • Concentration Dependency: The absorbance is directly proportional to the concentration of molecules in the sample, as it depends on the number of excited electrons.
  • Detection: Detectors in the spectrometer capture the absorption spectrum, providing information about the sample’s composition and concentration.
• Steps of UV Spectroscopy:
  • Sample Preparation: Known and unknown samples are prepared and placed in transport vessels called cuvettes.
  • Instrument Setup: The cuvettes are inserted into the spectrophotometer equipped with a light source and detectors.
  • Light Transmission: The spectrophotometer passes UV light of a specific wavelength through the sample.
  • Detection: Photosensitive detectors measure the light transmitted through the sample, converting it into digital values.
  • Data Analysis: A graph of absorbance versus sample concentration is plotted, allowing for the determination of the unknown sample’s concentration.
• Uses of UV Spectroscopy:
  • Impurity Detection: UV spectroscopy is utilized for detecting impurities in organic substances, as impurities often absorb UV radiation differently from the main compound.
  • Quantitative Analysis: It enables the quantitative determination of compounds that absorb UV radiation, such as aromatic compounds, by measuring absorbance.
  • Kinetics Studies: UV spectroscopy is used to study reaction kinetics by monitoring changes in absorbance as the reaction progresses, providing insights into reaction rates and mechanisms.

5. Ultraviolet and visible (UV/Vis) spectroscopy

• Ultraviolet and visible (UV/Vis) spectroscopy is a fundamental technique in analytical chemistry that utilizes the absorption of electromagnetic radiation in the UV and visible ranges to provide insights into the composition and concentration of substances. Here’s an overview of its principle, steps, and applications:
• Principle of UV/Vis Spectroscopy:
  • Absorption Spectrum Formation: UV/Vis spectroscopy relies on the generation of an absorption spectrum, which represents the range of wavelengths at which a material absorbs radiation.
  • Molecular Composition Dependency: The absorption spectrum of a substance is determined by its atomic and molecular composition.
  • Energy State Transition: When UV or visible light is absorbed by a material, electrons are excited from lower to higher energy states.
  • Absorption Line Formation: This excitation leads to the formation of absorption lines in the spectrum, with each line corresponding to a specific electronic transition.
  • Measurement of Absorbance: The amount of absorbed radiation, known as absorbance, is quantified and used to analyze the concentration of molecules in the sample.
• Steps of UV/Vis Spectroscopy:
  • Sample Preparation: Samples are prepared in solution form and placed in cuvettes, along with solvent as reference.
  • Baseline Correction: The cuvette containing only the solvent is analyzed to establish a baseline, accounting for scattering and solvent absorbance.
  • Sample Analysis: The cuvette containing the sample solution is inserted into the spectrometer, and absorbance is measured across a range of wavelengths (typically 200-800 nm).
  • Data Collection: Absorbance data is collected and used to generate an absorbance spectrum for the sample.
  • Quantitative Analysis: A calibration curve is often constructed using samples of known concentration to determine the concentration of the unknown sample.
• Uses of UV/Vis Spectroscopy:
  • Qualitative Analysis: UV/Vis spectroscopy can identify certain classes of compounds, such as proteins and nucleic acids, both in pure form and in biological mixtures.
  • Quantitative Analysis: It is widely used for the quantification of biological samples, either directly or through colorimetric assays.
  • Pharmaceutical Analysis: UV/Vis spectroscopy is employed in pharmaceutical industries to analyze drug formulations and monitor drug stability.
  • Environmental Monitoring: It is utilized for monitoring environmental pollutants, such as heavy metals and organic compounds, in water and air samples.

6. X-ray photoelectron spectroscopy

• X-ray Photoelectron Spectroscopy (XPS) is a powerful analytical technique used to determine the elemental composition, chemical state, and electronic structure of materials, especially surfaces. Here’s an overview of its principle, steps, and applications:
• Principle of X-ray Photoelectron Spectroscopy:
  • Photoelectric Effect: XPS is based on the photoelectric effect, where X-rays with specific wavelengths are directed onto a sample, causing the ejection of photoelectrons from its surface.
  • Binding Energy Determination: The energy of these emitted photoelectrons is characteristic of the elements present and their chemical states within the sample.
  • Binding Energy Calculation: The binding energy (BE) of the electrons is determined using the equation: BE = hν – KE, where hν is the energy of the incident X-ray photons and KE is the kinetic energy of the emitted photoelectrons.
  • Spectral Analysis: A plot of the binding energy versus the intensity of emitted electrons reveals peaks corresponding to different elements and their electronic configurations.
• Steps of X-ray Photoelectron Spectroscopy:
  • Sample Preparation: The sample is cleaned to remove surface contaminants and placed in the XPS instrument’s vacuum chamber.
  • X-ray Exposure: X-rays of specific energies are directed onto the sample surface, causing the ejection of photoelectrons.
  • Detection and Analysis: The emitted photoelectrons are detected by an electron energy analyzer, which measures their kinetic energies.
  • Data Interpretation: The resulting spectra are analyzed to determine the binding energies of the photoelectrons, which provide information about the elemental composition and chemical environment of the sample.
  • Elemental Identification: Peaks in the spectra correspond to different elements present in the sample, allowing for the identification of elements and their chemical states.
• Uses of X-ray Photoelectron Spectroscopy:
  • Material Characterization: XPS is widely used to analyze the elemental composition and chemical states of surfaces and thin films in materials science and engineering.
  • Surface Chemistry Studies: It provides valuable insights into surface reactions, adsorption phenomena, and catalytic processes.
  • Semiconductor Analysis: XPS is employed in the semiconductor industry for quality control, surface modification studies, and device fabrication.
  • Biomedical Applications: XPS is utilized in biomedical research for studying biomaterials, surface coatings, and implant surfaces.

7. Fourier-transform infrared (FTIR) spectroscopy

• Fourier-transform infrared (FTIR) spectroscopy is an instrumental technique employed for the identification and analysis of infrared spectra, showcasing the absorption and emission patterns of molecules in various phases, including liquids, solids, and gases. The term “Fourier-transform” denotes the mathematical algorithm utilized to convert raw data into the final spectrum.
• Principle of FTIR Spectroscopy: FTIR spectroscopy operates on the principle of dispersive spectroscopy, wherein a beam of light containing multiple frequencies is directed at the sample. The extent to which the sample absorbs this beam is measured, utilizing a second beam with different frequencies for comparison. This process is repeated multiple times within a short period. The collected data are then processed using Fourier transform, a mathematical technique that extracts the underlying frequencies from the raw data. The spectrometer typically features a Michelson interferometer, comprising mirrors, one of which is moved toward the light source. As the moving mirror blocks and transmits light waves, interference patterns emerge, resulting in a distinct spectrum for each measurement.
• Steps of FTIR Spectroscopy:
  • Sample Preparation: The sample, typically in a thin form allowing infrared light penetration, is placed into the FTIR spectrometer.
  • IR Light Exposure: The spectrometer directs infrared (IR) light onto the sample, measuring the extent and frequencies of beam absorption.
  • Data Analysis: The collected data are processed using Fourier transform to generate the final spectrum. Online reference databases aid in sample identification.
• Uses of FTIR Spectroscopy:
  • Chemical Analysis: FTIR spectroscopy finds extensive use in studying organic, polymeric, and inorganic compounds, enabling precise measurement of chemical content.
  • Substance Identification: It is often employed alongside gas chromatography to identify substances that are not chromatographically separated, enhancing analytical capabilities.
  • Study of Membranes: FTIR can determine the polarity of specific locations within hydrophobic membranes, aiding in membrane characterization and understanding.

8. Gamma-ray spectroscopy

• Gamma-ray spectroscopy serves as a vital analytical technique utilized to study the energy spectrum of gamma rays emitted by radioactive substances within a sample.
• Principle of Gamma-ray Spectroscopy: During the process of radioactive decay, gamma decay occurs alongside other forms of decay. In gamma decay, nucleons within the nucleus transition to lower energy states, emitting gamma rays in the process. These gamma rays are then directed through detectors, which convert the radiation into electrical signals for analysis by a computer. By detecting and quantifying gamma rays, researchers can discern the nature of the radioactive source. Comparison of the measured energy levels with the known energies of gamma rays produced by specific radioisotopes allows for the identification of the emitter.
• Steps of Gamma-ray Spectroscopy:
  • Preparation of Counting Chamber: The counting chamber, often shielded with lead and lined with copper to minimize background radiation, is prepared.
  • Sample Placement: The sample container is carefully positioned atop the detector within the counting chamber, which is then sealed.
  • Background Counting: Background counting is conducted to assess any contamination or natural radiation that may interfere with the sample data.
  • Data Analysis: The data collected from the detectors are analyzed using computing systems to determine the energy spectrum of gamma rays emitted by the sample.
• Uses of Gamma-ray Spectroscopy:
  • Nuclear Structure and Reactions: Gamma-ray spectroscopy is predominantly employed for the study of nuclear structure, transitions, and reactions, providing valuable insights into the behavior of atomic nuclei.
  • Astronomical Research: In astronomy, gamma-ray spectroscopy aids in the detection of water and other substances on celestial bodies, contributing to our understanding of planetary composition.
  • Elemental and Isotopic Analysis: It is utilized for the elemental and isotopic analysis of airless bodies within the solar system, such as the Moon and Mars, offering insights into their composition and geological history.

9. Circular dichroism spectroscopy

• Principle: The fundamental principle behind CD spectroscopy lies in the differential absorption of left- and right-handed circularly polarized light by optically active substances. This phenomenon, known as circular dichroism, arises because chiral molecules have distinct absorption coefficients for these two forms of light, often resulting in different propagation speeds through the medium. In biological molecules like proteins, specific bonds such as peptide bonds serve as chromophores, absorbing circularly polarized light in a manner that reflects their structural conformation.
• Methodology:
  • Sample Preparation: Initially, the sample of interest, such as a protein solution, is prepared and placed in a cuvette along with appropriate buffers to maintain stability.
  • Illumination: Within the spectrometer, the sample is exposed alternately to left and right circularly polarized light. This is achieved using specific optical components that modify the polarization state of the incident light beam.
  • Detection: As the polarized light passes through the sample, a detector, typically a photomultiplier tube, measures the intensity of the transmitted light. The key metric here is the difference in absorbance between the left and right polarized light, which is proportional to the circular dichroism exhibited by the sample.
  • Analysis: The resulting CD spectrum, which plots the differential absorbance against wavelength, is then analyzed. By comparing the CD spectrum of the sample with those of standard or known structures, one can infer the secondary structure content, such as the proportions of α-helices and β-sheets in a protein.
• Applications:
  • Structural Analysis of Biomolecules: The primary use of CD spectroscopy is in determining or confirming the secondary structures of proteins and other biomolecules. The technique is sensitive to the presence of specific structural motifs like α-helices and β-sheets, making it invaluable for understanding protein folding and conformation.
  • Monitoring Structural Changes: CD spectroscopy can track changes in the secondary structure of biomolecules over time, under varying conditions, or in response to ligand binding. This application is crucial for studying protein dynamics, folding mechanisms, and interactions.
  • Comparative Studies: By comparing the CD spectra of different macromolecules or the same molecule under different conditions, researchers can detect and quantify structural differences. This is particularly useful in comparative studies of wild-type and mutant proteins or in the analysis of protein-protein and protein-ligand interactions.
  • Pharmaceutical Analysis: In the pharmaceutical industry, CD spectroscopy helps ensure the proper folding and conformation of therapeutic proteins and other biologically active molecules, which is critical for their efficacy and stability.

10. Electrochemical impedance spectrum (EIS)

• Principle: The essence of EIS lies in its ability to assess how a material or device hinders the flow of electric current. By introducing an AC signal to the sample through electrodes, and varying the frequency of this signal, EIS captures the material’s response in terms of current flow. The resulting data, encompassing both the amplitude and phase shift of the current relative to the applied voltage, are used to calculate the real and imaginary components of impedance. These components reflect the resistive and capacitive behavior of the system, respectively. The relationship between impedance and frequency is often visualized in a Nyquist plot, where impedance is plotted against frequency, providing a comprehensive overview of the electrochemical dynamics at play.
• Steps:
  • System Setup: Initially, the experimental setup is validated using a test module to ensure proper connection and functionality of all components.
  • Parameter Configuration: The EIS measurement is configured using specialized software, such as Zplot, where parameters like AC amplitude and frequency range are set according to the requirements of the experiment.
  • Measurement Execution: With the parameters set, the EIS system applies an AC potential to the sample, and the resultant current is measured across the specified frequency range.
  • Data Analysis: The collected data are analyzed using software like Zview, which helps in interpreting the impedance spectra and extracting meaningful information about the sample’s electrochemical properties.
  • Sample Preparation and Testing: The actual sample is then prepared, positioned within the test setup (e.g., a furnace for high-temperature experiments), and subjected to EIS analysis following the established procedures.
• Uses:
  • Microbial Growth Detection: In biological applications, EIS can monitor the growth of microorganisms by detecting changes in impedance, which correlates with the cell population density in a sample.
  • Cancer Tissue Screening: The technique has shown promise in medical diagnostics, particularly in distinguishing cancerous tissues from healthy ones, based on the variation in electrical impedance attributed to differences in cellular structure and composition.
  • Material Coating Analysis: In materials science, EIS is extensively used to study the electrochemical properties of surface coatings, polymers, and chemical layers applied to electrodes. This application is crucial for developing more efficient and sensitive electrochemical sensors and devices.

11. Electron spin resonance (ESR)

• Principle: At the heart of ESR spectroscopy is the principle that atoms, molecules, or ions harboring unpaired electrons inherently possess magnetic properties due to the spin of these electrons. In the presence of an external magnetic field, these unpaired electrons can align in two distinct states: parallel (lower energy) or antiparallel (higher energy) to the field. The transition between these two states can occur through the absorption or emission of photons, matching the energy difference between the states. This phenomenon creates a resonance condition, detectable as an ESR spectrum, which provides insightful information regarding the electronic structures of the sample.
• Methodology:
  • Instrument Preparation: The ESR spectrometer is preheated and stabilized, typically requiring around 30 minutes. Setting the correct parameters is crucial for accurate measurement.
  • Calibration: To ensure the reliability of the data, the instrument is calibrated using an empty ESR tube, eliminating potential background signals from the apparatus or the tube itself.
  • Sample Analysis: The sample of interest is placed within the ESR tube, which is then inserted into the spectrometer. The instrument measures the ESR spectrum, capturing the resonance peaks indicative of transitions between the magnetic energy levels of the unpaired electrons.
• Applications:
  • Metalloprotein Studies: ESR spectroscopy is instrumental in investigating metalloproteins, especially those containing transition metals, by elucidating their electronic and structural characteristics.
  • Protein Folding and Denaturation: The technique offers a window into the processes of protein folding and denaturation, providing clues about the structural changes occurring within proteins.
  • Catalysis Rate Determination: ESR can be used to assess the catalytic activities of various metals, aiding in the understanding of reaction mechanisms and the development of catalysts.
  • Biological Research: In the biological domain, ESR spectroscopy is valuable for the quantitative and qualitative analysis of reactive species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), which play critical roles in various physiological and pathological processes.

12. Fluorescence spectroscopy

• Fluorescence spectroscopy stands as a powerful analytical technique within the realm of electromagnetic spectroscopy, harnessing the phenomenon of fluorescence emitted by substances in response to excitation by light.
• Principle: The principle of fluorescence spectroscopy parallels that of emission spectroscopy, where transitions of electrons between energy states lead to the emission of radiation. In fluorescence, molecules absorb light energy, promoting electrons to higher energy states. As these electrons return to lower energy states, they emit photons, resulting in fluorescence. Notably, only molecules in their excited state can emit fluorescence, necessitating their prior excitation to higher energy levels. The emitted radiation appears as bands due to closely related wavelengths, dependent on rotational and vibrational energy levels. The fluorescence spectrum mirrors the absorption spectrum, with transitions governed by the intensity of the excitation light. The fluorescence properties of molecules aid in identifying their composition.
• Methodology:
  • Sample Preparation: Samples of known and unknown concentrations are collected in transport vessels, typically cuvettes.
  • Instrument Setup: The cuvettes are sequentially placed in a spectrofluorimeter equipped with detectors and a light source.
  • Excitation and Detection: The spectrofluorimeter emits light of a specific wavelength through the sample. Photosensitive detectors within the instrument detect the fluorescence emitted by the sample, converting it into digital data.
  • Data Analysis: The intensity of fluorescence is measured and plotted against the concentration of the sample. This graph enables the determination of the concentration of the unknown sample.
• Applications:
  • Medical and Biomedical Research: Fluorescence spectroscopy finds extensive applications in medical and biomedical research, aiding in the study and analysis of organic chemicals. It is particularly useful in differentiating benign tumors from malignant ones.
  • Environmental Analysis: The technique is employed to determine the presence of various metals in environmental samples, including water, air, and soil, contributing to environmental monitoring and assessment efforts.
  • Analytical Chemistry: Fluorescence detectors are utilized in conjunction with High-Performance Liquid Chromatography (HPLC) in analytical chemistry, facilitating the analysis of complex mixtures and compounds.

13. Mossbauer spectroscopy

• Mossbauer spectroscopy, based on the Mossbauer effect discovered by Rudolf Mössbauer, is a powerful technique that analyzes the spectrum formed by the absorption or emission of nuclear gamma rays in solid particles.
• Principle of Mossbauer Spectroscopy:
  • Mossbauer Effect: The Mossbauer effect describes the recoil energy associated with the absorption or emission of a photon, governed by the conservation of momentum.
  • Solid-State Nuclei: In solid particles, atomic nuclei are bound to a lattice. When these nuclei emit or absorb gamma rays, energy is lost in discrete packets called phonons, representing quantized lattice vibrations.
  • Conservation of Momentum: Sometimes, no phonons are released, and momentum conservation is maintained by the lattice as a whole.
  • Gamma Ray Absorption: Gamma rays emitted by one nucleus can be completely absorbed by a sample containing nuclei of the same isotope, allowing for precise measurement.
• Steps of Mossbauer Spectroscopy:
  • Sample Preparation: Place the sample inside the spectrometer, ensuring that the atoms in the radiation source emitting gamma rays have the same isotope as those in the sample.
  • Gamma Ray Beam: Pass a beam of gamma radiation through the sample.
  • Intensity Measurement: Measure the intensity of the gamma ray beam transmitted through the sample.
  • Analysis: Analyze the resulting spectrum to extract information about the chemical, structural, and magnetic properties of the sample.
• Uses of Mossbauer Spectroscopy:
  • Sensitive Detection: Mossbauer spectroscopy can detect subtle changes in the nuclear environment, providing precise information about the sample.
  • Chemical and Structural Analysis: It offers insights into the chemical composition, structure, and magnetic properties of various materials.
  • Geological Applications: Used in geology to analyze the composition of meteors and moon rocks.
  • Bioorganic Chemistry: Widely applied in the study of iron-containing proteins and enzymes, providing valuable data for bioorganic research.

14. NMR spectroscopy (NMR) analysis of spectroscopy

• Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique that exploits the magnetic properties of atomic nuclei to elucidate the structure and dynamics of molecules.
• Principle of NMR Spectroscopy:
  • Nuclear Spin: NMR spectroscopy relies on the inherent spin of atomic nuclei, which behave like tiny magnets.
  • Magnetic Field Alignment: When a sample is placed in a strong magnetic field, the nuclear spins align either parallel or antiparallel to the field.
  • Resonance Condition: By applying radiofrequency (RF) radiation, nuclei can be flipped between these two states, causing them to absorb energy and resonate.
  • Detected Signals: The absorbed energy is detected as signals in the NMR spectrum, providing information about the chemical environment and interactions of the nuclei.
• Steps of NMR Spectroscopy:
  • Instrument Setup: The NMR instrument is initialized and allowed to stabilize, ensuring optimal performance.
  • Calibration: An empty NMR tube is inserted to calibrate the instrument and remove any background signals.
  • Sample Preparation: The sample of interest is dissolved in a suitable solvent and placed in an NMR tube.
  • Data Acquisition: The NMR spectrum is acquired by subjecting the sample to RF radiation and detecting the resulting signals.
  • Analysis: The spectrum is analyzed to interpret chemical shifts, peak intensities, and coupling patterns, providing information about molecular structure and dynamics.
• Uses of NMR Spectroscopy:
  • Quality Control: NMR spectroscopy is widely used in industries such as pharmaceuticals and food science for quality control purposes, ensuring the purity and authenticity of products.
  • Structural Elucidation: It is invaluable for determining the structure of organic and inorganic molecules, including complex natural products and synthetic compounds.
  • Solid-State NMR: In addition to solution-state NMR, solid-state NMR spectroscopy is employed to study the molecular structure of solids, polymers, and materials.
  • Protein Structure Determination: NMR spectroscopy plays a crucial role in structural biology by providing atomic-level insights into the three-dimensional structures of proteins and nucleic acids.

15. Photoelectron spectroscopy

• Photoelectron spectroscopy, also known as photoemission spectroscopy, is a powerful analytical technique used to study the electronic structure of materials by measuring the energy of electrons emitted from a sample upon exposure to ultraviolet (UV) or X-ray radiation. Here’s an overview of its principle, steps, and uses:
• Principle of Photoelectron Spectroscopy:
  • Photoelectric Effect: Photoelectron spectroscopy relies on the photoelectric effect, where photons from a radiation source dislodge electrons from the surface of a material.
  • Binding Energies: Electrons emitted during photoionization carry kinetic energy (KE) that depends on the energy of the incident photons (hν) and the binding energy (BE) of the electrons within the material.
  • Energy Analysis: By measuring the kinetic energy of emitted electrons, one can deduce the binding energies of electrons in different energy levels and orbitals of atoms within the sample.
  • Spectral Analysis: Plotting the binding energy against the kinetic energy yields a photoelectron spectrum, with peaks corresponding to electrons from different atomic orbitals.
• Steps of Photoelectron Spectroscopy:
  • Sample Preparation: The sample is cleaned and mounted in the spectrometer under vacuum conditions to prevent interference from air molecules.
  • Radiation Exposure: The sample is irradiated with UV or X-ray radiation, causing photoionization and the emission of electrons.
  • Electron Detection: Emitted electrons are collected and accelerated towards detectors, where their kinetic energies are measured.
  • Data Acquisition: The energy of emitted electrons is recorded, and a photoelectron spectrum is generated by plotting binding energies against kinetic energies.
  • Analysis: Peaks in the spectrum correspond to different electronic states of atoms in the sample, providing valuable information about its electronic structure.
• Uses of Photoelectron Spectroscopy:
  • Material Characterization: Photoelectron spectroscopy is widely used to investigate the electronic properties of solids, surfaces, and thin films, aiding in material characterization and surface analysis.
  • Chemical Analysis: It provides detailed information about the chemical composition, bonding, and oxidation states of elements within a sample, making it valuable for chemical analysis.
  • Surface Science: Photoelectron spectroscopy is essential in surface science, where it is used to study surface reactions, adsorption, and catalysis on solid surfaces.
  • Semiconductor Research: It is employed in semiconductor research for analyzing electronic structures, interfaces, and defects in semiconductor materials.

16. Infrared (IR) spectrum/ vibrational analysis

• Infrared (IR) spectroscopy, also known as vibrational spectroscopy, is a technique that explores the interaction between infrared rays and a sample, providing valuable insights into its molecular structure.
• Principle of IR Spectrum/Vibrational Analysis: The infrared spectrum typically covers wavelengths ranging from 2,500 to 16,000 nanometers and frequencies between 1.9×10^13 to 1.2×10^14 Hertz. Unlike ultraviolet or visible light, infrared rays lack sufficient energy to excite electrons. Instead, they induce vibrational excitations in the covalently bonded atoms and groups within the sample. The characteristic vibrational modes exhibited by different atoms and functional groups aid in the identification of molecules. The IR spectrum, a fundamental measurement in infrared spectroscopy, depicts the intensity of infrared radiation against its frequency. By analyzing the frequency and vibrations of atoms, functional groups within the molecule can be identified.
• Steps of IR Spectrum/Vibrational Analysis:
  • Instrument Preparation: The IR spectrometer is powered on and allowed to warm up for approximately 30 minutes.
  • Sample Handling: The unknown sample is collected, and its appearance is recorded for reference.
  • Background Spectrum Collection: A background spectrum is acquired to eliminate any interference from natural causes.
  • Sample Placement: A small portion of the sample is placed in the probe using a metal spatula.
  • Spectrum Acquisition: The probe is positioned, and the IR spectrum of the unknown sample is recorded. This process may be repeated to ensure a satisfactory quality spectrum.
  • Absorption Frequencies Recording: Absorption frequencies corresponding to functional groups present in the sample are noted.
  • Spectrum Analysis: The obtained spectrum is analyzed to deduce the likely identity of the unknown sample.
• Applications of IR Vibrational Spectroscopy:
  • Material Characterization: Infrared spectroscopy is widely used to characterize various materials, including proteins and solid, liquid, and gaseous samples.
  • Functional Group Detection: IR spectroscopy detects characteristic functional groups, aiding in the identification of molecules and their components.
  • Biomedical Applications: IR spectroscopy is employed in biomedical research to understand molecular changes associated with diseases and to identify specific biomarkers for diagnosis.

17. Magnetic resonance spectroscopy

• Magnetic resonance spectroscopy (MRS) is a diagnostic technique closely related to magnetic resonance imaging (MRI), focusing on the measurement of biochemical changes occurring within various tissues of the body.
• Principle of Magnetic Resonance Spectroscopy: Magnetic resonance spectroscopy involves the analysis of hydrogen atoms present within the sample under study. When subjected to a magnetic field, the nucleus of the hydrogen atom becomes excited, causing it to spin in a particular direction. This spinning process generates characteristic spectra based on the energy differences associated with different spin directions. By examining the frequencies within these spectra, the concentration of various metabolites can be determined. Comparing these concentrations to normal levels found in different cells allows for the identification of specific tissue types within the body.
• Steps of Magnetic Resonance Spectroscopy:
  • Instrument Setup: The MR instrument is powered on and allowed to warm up for approximately 30 minutes. Necessary parameters are configured in the magnetic resonance spectrometer.
  • Calibration: Calibration is performed to ensure accurate measurements. An empty MR tube is inserted to verify that no background signals are interfering with the readings.
  • Sample Preparation: The sample under investigation is placed within the MR tube, ensuring it is properly positioned for analysis.
  • Data Acquisition: The magnetic resonance spectrum of the sample is then measured using the spectrometer. This process captures the characteristic frequencies associated with the metabolites present.
• Uses of Magnetic Resonance Spectroscopy:
  • Diagnostic Information: MRS provides valuable biochemical information about tissue composition, aiding in the diagnostic process for various medical conditions.
  • Complementary to MRI: MRS complements MRI by offering additional insights into tissue metabolism and composition, enhancing the diagnostic capabilities of medical professionals.
  • Research Applications: Magnetic resonance spectroscopy is widely used in medical research projects, contributing to the understanding of disease mechanisms and potential treatment options.
  • Metabolic Profiling: In specific cases, such as hepatocellular carcinoma (HCC), MRS has been utilized to create metabolic profiles of serum samples from diagnosed patients, offering valuable insights into disease progression and treatment response.

18. Mass spectroscopy

• Mass spectroscopy is a powerful analytical technique utilized to identify the quantity and composition of chemicals present within a sample by analyzing the mass-to-charge ratio of ions.
• Principle of Mass Spectroscopy: Mass spectroscopy operates on the principle of ionization, where a sample is bombarded with electrons, causing its molecules to become ionized into ions. These ions are then separated based on their mass-to-charge ratio.
  • Ionization: Electrons bombard the sample, ionizing its molecules into ions.
  • Ion Separation: Ions are subjected to electric and magnetic fields, causing them to deflect. Ions with similar mass-to-charge ratios exhibit similar deflection patterns.
  • Detection: The relative abundance of ions is detected using detectors.
  • Mass Spectrum Formation: The relative abundance of ions is plotted against the mass-to-charge ratio, forming the mass spectrum.
  • Analysis: The mass spectrum is analyzed to determine the elemental configuration, masses of particles or molecules, and chemical structure of the sample.
• Steps of Mass Spectroscopy:
  • Sample Preparation: The sample is prepared by mixing it with a suitable solvent or buffer.
  • Ionization: The prepared sample is bombarded with electrons to ionize its molecules.
  • Separation and Detection: Ions are separated based on their mass-to-charge ratios and detected by the spectrometer.
  • Data Analysis: The obtained data is analyzed using software to generate the mass spectrum.
• Uses of Mass Spectroscopy:
  • Quantification: Mass spectroscopy is used to quantify known materials accurately.
  • Identification: It facilitates the identification of unknown compounds present in a sample.
  • Structural Analysis: Mass spectroscopy helps determine the chemical structure and composition of various substances.
  • Quality Control: It is employed in quality control processes across industries, including pharmaceuticals, food, and environmental analysis.

19. Emission spectroscopy

• Principle: The principle underlying emission spectroscopy is based on the phenomenon of emission of photons by atoms or molecules when they transition from excited to ground states. This emission occurs when the sample is excited, typically by heating in a flame or using an electric heater. As electrons return to lower energy levels, they release energy in the form of light. This emitted light is then passed through a spectrometer, which disperses it into its constituent wavelengths. Each element emits light at specific wavelengths, characteristic of its electronic structure. By analyzing these emitted wavelengths, the elemental composition of the sample can be deduced.
• Methodology:
  • Sample Excitation: The sample, usually in solution form, is heated in a flame or with an electric heater. As the sample is heated, the solvent evaporates, leaving behind finely divided solid particles.
  • Excitation and Emission: The heating process excites electrons within the sample, causing them to transition to higher energy levels. As these electrons return to lower energy levels, they emit photons of specific wavelengths characteristic of the element.
  • Spectrometer Analysis: The emitted radiation is directed into a spectrometer, where a monochromator disperses the light into its constituent wavelengths. Detectors within the spectroscope then detect these wavelengths.
  • Data Analysis: A graph of wavelength against intensity or concentration is plotted based on the detected wavelengths. This graph enables the determination of the elemental composition or concentration of the sample.
• Applications:
  • Analytical Chemistry: Emission spectroscopy finds wide applications in analytical chemistry for the detection and quantification of metals and alloys. It is extensively used in agricultural, environmental, and industrial analyses.
  • Lead Determination in Petrol: In environmental analysis, emission spectroscopy is employed for the determination of lead levels in petrol, contributing to regulatory compliance and environmental protection efforts.
  • Equilibrium Constant Determination: The technique has also been applied in determining the equilibrium constants of ion exchange resins, aiding in the understanding of chemical equilibrium processes.

20. Energy dispersive spectrum

• Energy Dispersive Spectroscopy (EDS), also known as Electron Dispersive X-ray Spectroscopy, serves as a valuable analytical technique for the elemental or chemical characterization of samples, leveraging the interaction of X-rays with the material.
• Principle: The underlying principle of EDS is akin to emission spectroscopy, albeit with X-ray beams serving as the excitation source. When X-rays are directed at a sample, they interact with the electrons in the atoms of the material. These interactions lead to the excitation of electrons from the ground state to higher energy levels, typically inner electron shells. As electrons transition back to lower energy levels, they leave behind electron vacancies or “holes” in the outer shells, which are then filled by electrons from higher energy shells. The energy difference between these shells is emitted in the form of characteristic X-ray beams. By detecting and analyzing these X-rays, EDS determines their energy and quantity, providing insights into the elemental composition of the sample based on the characteristic energies of the emitted X-rays.
• Methodology:
  • Sample Preparation: Samples of known and unknown concentrations are prepared and placed in a transport vessel, such as a cuvette.
  • Instrument Setup: The transport vessels are sequentially placed in the spectrophotometer, which includes an excitation source, such as an electron beam or X-ray beam, and detectors.
  • X-ray Excitation: The spectrophotometer directs X-rays through the sample, causing interactions that result in the emission of characteristic X-ray beams.
  • Detection and Analysis: Photosensitive detectors within the spectrophotometer detect the emitted X-rays, converting them into voltage signals. These signals are then processed by a pulse processor, which measures and analyzes the signals. The data are subsequently displayed and further analyzed by an analyzer.
• Applications:
  • Materials Science and Research: EDS, as a component of electron microscopy, finds extensive use in various research areas, providing precise information on the chemical composition of materials at the microscale.
  • Medical Diagnostics: In medical diagnostics, X-ray microanalysis facilitated by EDS aids in defining criteria for malignant tissue formation, contributing to diagnostic accuracy and patient care.
  • Environmental Analysis: EDS serves as a valuable tool in environmental analysis, enabling the estimation of the health risks associated with polluted air by analyzing the elemental composition of airborne particles.
  • Pesticide Analysis: The technique can also be applied to analyze pesticide droplets deposited on plant surfaces, aiding in pesticide monitoring and environmental impact assessment.

21. Molecular spectroscopy

• Molecular spectroscopy is a fundamental analytical technique that leverages the interaction between molecules and electromagnetic radiation to unveil the structural composition of samples.
• Principle of Molecular Spectroscopy: Molecular spectroscopy revolves around the interaction of materials with electromagnetic radiation, yielding absorption patterns (spectra) that provide valuable structural and compositional insights.
  • Energy State Transition: Molecules transition between different energy states upon interaction with electromagnetic radiation, resulting in the formation of molecular spectra.
  • Types of Interactions: Molecular interactions include electronic, rotational, and vibrational transitions, each revealing unique information about the molecule’s structure and composition.
  • Absorption and Emission: Molecular spectroscopy can exploit both absorption and emission spectra, depending on the nature of the interactions being studied.
• Steps of Molecular Spectroscopy:
  • Instrument Setup: Utilize various spectrometer systems such as emission spectrometers or Fourier-transform spectrometers.
  • Sample Preparation: Place the sample in the spectrometer, where it interacts with the radiation source.
  • Measurement: Pass light of specific wavelengths through the sample and detect the transmitted or emitted light using photosensitive detectors.
  • Data Analysis: Convert the detected signals into digital values and plot absorbance against the concentration of the sample.
  • Interpretation: Analyze the resulting spectra to deduce the unknown concentration or gain insights into the atomic and molecular structures of the compounds.
• Uses of Molecular Spectroscopy:
  • Structural Analysis: Molecular spectroscopy enables the analysis of atomic and molecular structures across various compounds.
  • Composition Determination: It aids in determining the composition of gases and other compounds, providing valuable information for research and industrial applications.
  • Chemical Identification: Molecular spectroscopy is invaluable in identifying unknown compounds and elucidating their chemical properties.
  • Quantitative Analysis: It facilitates quantitative analysis by correlating absorbance measurements with sample concentrations, allowing for accurate determination of compound concentrations.

22. Raman spectrum

• Raman spectroscopy is a valuable analytical technique used to examine the molecular composition and interactions within a substance. Here’s an overview of its principle, steps, and applications:
• Principle of Raman Spectroscopy:
  • Scattered Light Analysis: Raman spectroscopy involves the analysis of scattered light from a sample.
  • Incident Light: When a beam of light is directed onto a sample, the majority of it passes through (transmission), while a small fraction is scattered isotropically with the same wavelength as the incident beam.
  • Frequency Shift: A tiny portion of the scattered light experiences a change in frequency due to interactions with the molecular vibrations, rotations, and electronic transitions within the sample.
  • Energy Conservation: The energy difference between the scattered and incident photons corresponds to the energy change associated with the molecular vibrations, resulting in a Raman spectrum.
  • Polarizability Criterion: Peaks in the Raman spectrum occur when there is a change in the polarizability of the molecule during the transition, with depolarization ratio calculated to assess the orientation of the scattered light.
• Steps of Raman Spectroscopy:
  • Preparation: Aqueous solutions or samples are prepared, and the appropriate laser wavelength is selected.
  • Instrument Setup: The Raman spectrometer is calibrated using a reference sample to determine exposure energy and time.
  • Sample Placement: The sample is placed under the microscope, focusing on the area of interest.
  • Data Collection: The monochromator scans a range of wavenumbers, producing the Raman spectrum.
  • Analysis: Software is used to analyze the data, identifying peaks and interpreting the spectrum to determine molecular composition and interactions.
• Uses of Raman Spectroscopy:
  • Aqueous Conditions: Raman spectroscopy is advantageous over infrared spectroscopy for analyzing samples in aqueous conditions.
  • Chemical Analysis: It is widely used for determining the chemical composition, molecular structure, and polymorphism of materials.
  • Biomedical Applications: Raman spectroscopy has applications in biomedical research for studying cells, tissues, and biomolecules.
  • Pharmaceuticals: It is employed in the pharmaceutical industry for drug development, quality control, and formulation analysis.
  • Materials Science: Raman spectroscopy is valuable in materials science for investigating crystallinity, defects, and molecular interactions in various materials.

References

1. Atomic absorption spectroscopy
   • https://www.agilent.com/en/support/atomic-spectroscopy/atomic-absorption/flame-atomic-absorption-instruments/how-does-aas-work-aas-faqs
   • https://www.technologynetworks.com/analysis/articles/atomic-absorption-spectroscopy-principles-and-applications-356829
   • https://www.thermofisher.com/in/en/home/industrial/spectroscopy-elemental-isotope-analysis/spectroscopy-elemental-isotope-analysis-learning-center/trace-elemental-analysis-tea-information/atomic-absorption-aa-information.html
   • https://lab-training.com/aas/
2. Absorption spectroscopy
   • https://en.wikipedia.org/wiki/Absorption_spectroscopy#:~:text=Absorption%20spectroscopy%20is%20employed%20as,particularly%20common%20in%20analytical%20applications.
   • https://byjus.com/physics/absorption-spectrum/
   • https://www.sciencedirect.com/topics/materials-science/absorption-spectroscopy
   • https://study.com/academy/lesson/absorption-spectroscopy-definition-types.html
   • https://ibsen.com/technologies/absorption-spectroscopy/
   • https://chem.libretexts.org/Courses/University_of_Arkansas_Little_Rock/General_Chemistry_Lab_(Fall_2021)/00%3A_General_Information/4%3A_Instrumentation/3%3A_Absorbance_Spectroscopy
3. Astronomical spectroscopy
   • https://en.wikipedia.org/wiki/Astronomical_spectroscopy
   • https://www.worldscientific.com/worldscibooks/10.1142/7574#t=aboutBook
   • https://arxiv.org/abs/1010.5270
4. UV spectroscopy
   • https://www.technologynetworks.com/analysis/articles/uv-vis-spectroscopy-principle-strengths-and-limitations-and-applications-349865
   • https://en.wikipedia.org/wiki/Ultraviolet%E2%80%93visible_spectroscopy
   • https://www.sciencedirect.com/topics/chemistry/uv-vis-spectroscopy
5. Ultraviolet and visible (UV/Vis) spectroscopy
   • https://www.sciencedirect.com/topics/materials-science/x-ray-photoelectron-spectroscopy
   • https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy
   • https://mmrc.caltech.edu/XPS%20Info/Practical%20Guides%20to%20XPS/Intro%20to%20XPS.pdf
6. Fourier-transform infrared (FTIR) spectroscopy
   • https://rtilab.com/techniques/ftir-analysis/#:~:text=What%20is%20FTIR%3F,samples%20and%20observe%20chemical%20properties.
   • https://en.wikipedia.org/wiki/Fourier-transform_infrared_spectroscopy
   • https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/fourier-transform-infrared-spectroscopy
   • https://www.chem.uci.edu/~dmitryf/manuals/Fundamentals/FTIR%20principles.pdf
7. Gamma-ray spectroscopy
   • https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis/1.17%3A_Principles_of_Gamma-ray_Spectroscopy_and_Applications_in_Nuclear_Forensics
   • https://en.wikipedia.org/wiki/Gamma_spectroscopy
   • https://www.physlab.org/wp-content/uploads/2016/04/GammaExp-min.pdf
8. Circular dichroism spectroscopy
   • https://jascoinc.com/learning-center/theory/spectroscopy/circular-dichroism-spectroscopy/#:~:text=Circular%20Dichroism%20spectroscopy%20is%20a,optically%20active%20substances%20is%20measured.
   • https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electronic_Spectroscopy/Circular_Dichroism
   • https://en.wikipedia.org/wiki/Circular_dichroism
   • https://www.ntu.edu.sg/docs/librariesprovider12/default-document-library/circular-dichroism.pdf?sfvrsn=ec10f4d4_2
9. Electrochemical impedance spectrum (EIS)
   • https://pubs.acs.org/doi/10.1021/acsmeasuresciau.2c00070#:~:text=EIS%20is%20based%20on%20the,the%20system%20toward%20the%20applied
   • https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-spectroscopy/
   • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8512860/
   • https://www.palmsens.com/knowledgebase-article/electrochemical-impedance-spectroscopy-eis/
   • https://pineresearch.com/shop/kb/theory/eis-theory/eis-basics/
10. Electron spin resonance (ESR)
    • https://en.wikipedia.org/wiki/Electron_paramagnetic_resonance#:~:text=Electron%20paramagnetic%20resonance%20(EPR)%20or,instead%20of%20the%20atomic%20nuclei.
    • https://byjus.com/govt-exams/csir-net-electron-spin-resonance-esr-spectroscopy/
    • https://www.ccsuniversity.ac.in/ccsu/Departmentnews/2020-04-10_23.pdf
    • https://www.sciencedirect.com/topics/medicine-and-dentistry/electron-spin-resonance
11. Fluorescence spectroscopy
    • https://en.wikipedia.org/wiki/Fluorescence_spectroscopy
    • https://www.horiba.com/int/scientific/technologies/fluorescence-spectroscopy/what-is-fluorescence-spectroscopy/
    • https://www.chem.uci.edu/~dmitryf/manuals/Fundamentals/Fluorescence%20Spectroscopy.pdf
12. Other References
    • https://www.sciencedirect.com/topics/earth-and-planetary-sciences/mossbauer-spectroscopy#:~:text=M%C3%B6ssbauer%20spectroscopy%20stands%20for%20the,the%20lowest%20quantized%20vibrational%20mode.
    • https://en.wikipedia.org/wiki/M%C3%B6ssbauer_spectroscopy
    • https://byjus.com/chemistry/nmr-spectroscopy/#:~:text=What%20is%20NMR%20Spectroscopy%3F,in%20a%20strong%20magnetic%20field.
    • https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/spectrpy/nmr/nmr1.htm
    • https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_spectroscopy
    • https://www.technologynetworks.com/analysis/articles/nmr-spectroscopy-principles-interpreting-an-nmr-spectrum-and-common-problems-355891
    • https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:atomic-structure-and-properties/x2eef969c74e0d802:photoelectron-spectroscopy/a/photoelectron-spectroscopy#:~:text=Photoelectron%20spectroscopy%20(PES)%20is%20an,%E2%80%8D%20)%20of%20the%20ejected%20electrons.
    • https://en.wikipedia.org/wiki/Photoemission_spectroscopy
    • https://byjus.com/chemistry/photoelectron-spectrum/
    • https://www.pnnl.gov/explainer-articles/photoelectron-spectroscopy
    • https://en.wikipedia.org/wiki/Infrared_spectroscopy#:~:text=Infrared%20spectroscopy%20(IR%20spectroscopy%20or,%2C%20liquid%2C%20or%20gaseous%20forms.
    • https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Vibrational_Spectroscopy/Infrared_Spectroscopy/Infrared_Spectroscopy
    • https://sci.tanta.edu.eg/files/IR%20spectroscopy%20BSc-Lect-3.pdf
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4723643/
    • https://radiopaedia.org/articles/mr-spectroscopy-1
    • https://mayfieldclinic.com/pe-mrspectroscopy.htm
    • https://www.broadinstitute.org/technology-areas/what-mass-spectrometry#:~:text=Mass%20spectrometry%20is%20an%20analytical,the%20sample%20components%20as%20well.
    • https://byjus.com/chemistry/mass-spectrometry/
    • https://en.wikipedia.org/wiki/Mass_spectrometry
    • https://en.wikipedia.org/wiki/Emission_spectrum#:~:text=Emission%20spectroscopy%20is%20a%20spectroscopic,to%20a%20lower%20energy%20state.
    • https://byjus.com/physics/emission-spectrum/
    • https://www.sciencedirect.com/topics/materials-science/emission-spectroscopy
    • https://www.sciencedirect.com/topics/chemistry/energy-dispersive-spectroscopy#:~:text=The%20energy%20dispersive%20spectroscopy%20(EDS,being%20observed%20in%20SEM%20monitor.
    • https://en.wikipedia.org/wiki/Energy-dispersive_X-ray_spectroscopy
    • https://www.sciencedirect.com/topics/materials-science/molecular-spectroscopy#:~:text=Molecular%20spectroscopy%20is%20a%20subject,possible%20in%20a%20normal%20surrounding.
    • https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Molecular_and_Atomic_Spectroscopy_(Wenzel)/1%3A_General_Background_on_Molecular_Spectroscopy/1.1%3A_Introduction_to_Molecular_Spectroscopy
    • https://sci.tanta.edu.eg/files/Introduction%20Molecular%20Spectroscopy%20BSc-Lect%20-1.pdf
    • https://www.horiba.com/int/scientific/technologies/raman-imaging-and-spectroscopy/raman-spectroscopy/#:~:text=Raman%20Spectroscopy%20is%20a%20non,chemical%20bonds%20within%20a%20material.
    • https://www.edinst.com/blog/what-is-raman-spectroscopy/