An Introduction to Spectroscopy Techniques and Their Applications in Analysis
Spectroscopy is the study of the interaction between matter and electromagnetic radiation. It is a technique used to analyze the composition and structure of matter by examining how light or other electromagnetic radiation is absorbed, emitted, or scattered by that matter.
A spectrometer is an instrument used to measure spectra. It can split light into its constituent wavelengths and measure the intensity at each wavelength.
A spectrophotometer is a specific type of spectrometer that measures the intensity of light as a function of wavelength. It can be used to measure the absorption, transmission, or reflection of light.
A spectroscope is a simple spectrometer used to observe spectral lines and bands. It usually consists of a prism or diffraction grating to disperse light and view a spectrum.
A spectrograph is a spectroscope that can record the spectrum onto a photographic plate or detector. It produces a spectral graph or spectrogram.
Spectra refers to the characteristic patterns of frequencies/wavelengths in electromagnetic radiation emitted or absorbed by atoms and molecules. Each atom or molecule has a unique spectral signature.
Some key types of spectroscopy and their basic principles, steps, and uses:
1. Absorption Spectroscopy
- Principle: Based on the absorption of electromagnetic radiation by the analyte at characteristic wavelengths. The absorption follows Beer-Lambert law.
- Steps: 1) Shine light on sample, 2) Sample absorbs light at specific wavelengths, 3) Measure transmitted light intensity at different wavelengths, 4) Relate absorption to analyte concentration.
- Uses: Determine concentration of analytes, identify analytes, quantitative and qualitative analysis.
2. Astronomical Spectroscopy
- Principle: Analysis of electromagnetic radiation from stars and other celestial objects. Allows determination of chemical composition, motion, temperature, etc.
- Steps: 1) Light from celestial source dispersed into spectrum, 2) Sensitive detectors used to measure intensity at different wavelengths.
- Uses: Determine composition, temperature, radial velocity of astronomical objects.
3. Atomic Absorption Spectroscopy
- Principle: Sample is vaporized and light of specific wavelength is passed through vaporized atoms. Amount of light absorbed is proportional to analyte concentration.
- Steps: 1) Atomize sample, 2) Irradiate sample with light source specific to analyte, 3) Measure absorption.
- Uses: Quantitative determination of specific metal elements in samples.
4. Circular Dichroism Spectroscopy
- Principle: Differential absorption of left and right circularly polarized light due to structural asymmetry of molecules.
- Steps: 1) Irradiate sample with circularly polarized light, 2) Measure difference in absorption between left and right circularly polarized components.
- Uses: Study chiral molecules, determine protein secondary structure.
5. Electrochemical Impedance Spectroscopy
- Principle: Apply small amplitude AC signal to electrochemical cell and measure current response across a range of frequencies.
- Steps: 1) Apply AC potential to cell, 2) Measure current response as a function of frequency, 3) Analyze impedance spectrum.
- Uses: Study electrode processes and complex interfaces.
6. Electron Spin Resonance Spectroscopy
- Principle: Microwave absorption by unpaired electrons in a strong magnetic field. Provides information about electronic structure.
- Steps: 1) Place sample in magnetic field, 2) Irradiate sample with microwaves, 3) Detect microwave absorption as function of magnetic field.
- Uses: Study free radicals, identify paramagnetic species, examine properties of materials.
7. Emission Spectroscopy
- Principle: Excited atoms and molecules emit electromagnetic radiation at characteristic wavelengths as they relax.
- Steps: 1) Excite sample using heat/electrical energy, 2) Measure intensity of emitted light at different wavelengths.
- Uses: Identify elements, quantify analyte concentration, flame tests.
8. Energy Dispersive X-ray Spectroscopy
- Principle: X-rays emitted from a sample due to bombardment by electron beam are measured by energy.
- Steps: 1) Bombard sample with electron beam, 2) Detect emitted X-rays, 3) Measure X-ray energy spectra.
- Uses: Elemental analysis and chemical characterization of a sample.
9. Fluorescence Spectroscopy
- Principle: Fluorescent light is emitted from a sample after excitation by a light source.
- Steps: 1) Excite sample with light source, 2) Measure intensity and wavelengths of emitted fluorescent light.
- Uses: Analyze organic compounds, biochemical analysis, medical diagnostics.
10. Fourier Transform Infrared Spectroscopy
- Principle: Infrared light passing through a sample is measured by an interferometer to obtain an interferogram, which is decoded by Fourier transform.
- Steps: 1) Pass IR light through sample, 2) Measure interferogram, 3) Apply Fourier transform to get spectrum.
- Uses: Identify organic, polymeric, and some inorganic materials.
11. Gamma-ray Spectroscopy
- Principle: Nuclear transitions in atomic nuclei result in gamma-ray emissions at characteristic energies.
- Steps: 1) Excite sample to induce nuclear reactions, 2) Measure energy spectrum of emitted gamma-rays.
- Uses: Identify isotopes, analyze nuclear reactions.
12. Infrared Spectroscopy
- Principle: Infrared radiation excites molecular vibrations which absorb at specific wavelengths based on chemical structure.
- Steps: 1) Expose sample to IR radiation, 2) Measure IR absorption or transmission spectrum.
- Uses: Identify functional groups, analyze organic compounds, quantify components.
13. Magnetic Resonance Spectroscopy
- Principle: Atomic nuclei absorbed in a magnetic field absorb and re-emit electromagnetic radiation. Frequency depends on the nucleus and chemical environment.
- Steps: 1) Place sample in magnetic field, 2) Irradiate sample with radio waves, 3) Detect emitted radiation.
- Uses: Analyze molecular structure and chemical environment.
14. Mass Spectrometry
- Principle: Ions formed from a sample are separated based on mass-to-charge ratio.
- Steps: 1) Ionize analyte molecules, 2) Separate ions based on m/z, usually with electric/magnetic fields, 3) Detect ions.
- Uses: Identify unknown compounds, quantify molecules, determine molecular structure.
15. Molecular Spectroscopy
- Principle: Interaction of molecules with electromagnetic radiation at varying wavelengths is measured to derive structural and dynamic information.
- Steps: 1) Expose sample to EM radiation source, 2) Measure interaction (absorption, emission, scattering, etc.) as function of wavelength.
- Uses: Determine molecular structure, identify functional groups, analyze molecular motions/transitions.
16. Mössbauer Spectroscopy
- Principle: Based on recoil-free emission and absorption of gamma rays by atomic nuclei bound in a solid.
- Steps: 1) Irradiate sample with gamma rays, 2) Measure absorption spectrum of gamma rays.
- Uses: Study chemical environment and magnetic properties of iron-containing samples.
17. Nuclear Magnetic Resonance Spectroscopy
- Principle: Nuclei in a magnetic field absorb and re-emit electromagnetic radiation at characteristic frequencies.
- Steps: 1) Place sample in magnetic field, 2) Irradiate sample with radio waves, 3) Detect emitted radiation.
- Uses: Determine molecular structure, identify compounds, quantify analytes.
18. Photoelectron Spectroscopy
- Principle: High energy photons eject electrons from a sample. Kinetic energy measured provides information about elemental composition and chemical environment.
- Steps: 1) Irradiate sample with X-rays/UV rays, 2) Measure kinetic energy of emitted electrons.
- Uses: Determine elemental composition, chemical bonding, electronic structure.
19. Raman Spectroscopy
- Principle: Based on inelastic scattering of monochromatic light by molecules which provides vibrational info.
- Steps: 1) Illuminate sample with monochromatic source, 2) Measure frequency shifts in scattered light.
- Uses: Identify molecules, investigate sample composition.
20. UV Spectroscopy
- Principle: Samples absorb ultraviolet light at wavelengths corresponding to allowed electronic transitions.
- Steps: 1) Expose sample to UV light source, 2) Measure absorption spectrum in UV region.
- Uses: Quantify analytes, identify organic compounds, determine purity.
21. UV/Vis Spectroscopy
- Principle: Molecules containing π-electrons or non-bonding electrons can absorb UV/Vis light resulting in electronic transitions.
- Steps: 1) Expose sample to UV/Vis light, 2) Measure absorption spectrum.
- Uses: Quantify analytes using Beer-Lambert law, identify analytes, determine kinetics.
22. X-ray Photoelectron Spectroscopy
- Principle: X-ray irradiation causes photoelectron emission, with binding energies characteristic of each element.
- Steps: 1) Irradiate sample with X-rays, 2) Measure kinetic energy of emitted photoelectrons.
- Uses: Determine elemental composition, chemical states, electronic structure.
References:
- Skoog, Holler and Crouch - Principles of Instrumental Analysis
- Banwell and McCash - Fundamentals of Molecular Spectroscopy
- Hollas - Modern Spectroscopy
- McQuarrie - Quantum Chemistry
- Wilson and Walker - Principles and Techniques of Practical Biochemistry
- Günzler and Gremlich - IR Spectroscopy: An Introduction
