Definition of absorption spectroscopy

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Photonics Dictionary

absorption spectroscopy: Absorption spectroscopy is a fundamental analytical technique used to study the interaction between electromagnetic radiation and matter. It involves measuring the absorption of light by a sample across a range of wavelengths or frequencies. This absorption is caused by the sample's ability to absorb certain wavelengths of light, which corresponds to the excitation of electrons or molecules to higher energy levels.

Principle of absorption: Absorption occurs when the energy of incident photons matches the energy difference between the ground state and an excited state of the sample's constituents (such as atoms, molecules, or ions). The absorbed photons promote the sample's constituents to higher energy levels, leading to a reduction in the intensity of transmitted light. The amount of absorption depends on factors like the concentration of absorbing species, the path length of light through the sample, and the properties of the absorbing species.

Components of absorption spectroscopy:

Light source: A source of electromagnetic radiation, such as a lamp or laser, emits light across a range of wavelengths or frequencies.

Sample: The substance being analyzed, which absorbs specific wavelengths of light depending on its composition and properties.

Detector: A device capable of measuring the intensity of transmitted light as a function of wavelength or frequency.

Monochromator or spectrometer: An optical component that separates the incident light into its constituent wavelengths or frequencies, allowing for the determination of the absorption spectrum.

Reference cell: In some cases, a reference cell containing a solvent or blank solution may be used to calibrate the spectrometer and account for baseline absorbance.

Types of absorption spectroscopy:

Ultraviolet-visible (UV-Vis) spectroscopy: This technique measures absorption in the ultraviolet and visible regions of the electromagnetic spectrum (typically 200 to 800 nm). It is commonly used for analyzing organic compounds, transition metal complexes, and biological molecules.

Infrared (IR) spectroscopy: IR spectroscopy measures absorption in the infrared region of the spectrum (typically 4000 to 400 cm?¹). It is used for identifying functional groups in organic molecules and for analyzing polymers, drugs, and biomolecules.

Atomic absorption spectroscopy (AAS): AAS measures the absorption of light by individual atoms in the gas phase. It is widely used for elemental analysis in environmental, pharmaceutical, and clinical applications.

X-ray absorption spectroscopy (XAS): XAS measures the absorption of x-rays by atoms in a sample. It provides information about the electronic and geometric structure of materials and is used in materials science, catalysis, and environmental research.

Applications:

Quantitative analysis: Absorption spectroscopy is widely used for quantitative analysis of the concentration of absorbing species in a sample.

Qualitative analysis: It is used for identifying and characterizing compounds based on their absorption spectra.

Reaction monitoring: Absorption spectroscopy can be used to monitor chemical reactions in real-time by tracking changes in absorbance over time.

Biomedical and environmental monitoring: It is used in fields such as clinical diagnostics, environmental monitoring, and pharmaceutical analysis.

Advantages:

High sensitivity: Absorption spectroscopy can detect trace amounts of analytes.

Wide applicability: It can be applied to a wide range of samples, including gases, liquids, and solids.

Non-destructive: In many cases, absorption spectroscopy is non-destructive, allowing for the analysis of samples without altering their chemical composition.

Challenges:

Overlap of absorption bands: Overlapping absorption bands can make it challenging to identify and quantify individual components in complex samples.

Baseline drift: Baseline drift and instrument noise can affect the accuracy and precision of absorption measurements.

Sample preparation: Proper sample preparation is crucial to ensure accurate and reproducible results.

In summary, absorption spectroscopy is a versatile and widely used analytical technique that provides valuable information about the composition, structure, and properties of materials across various fields of science and technology.