Spectrometry is an analytical approach that examines the interaction between matter and electromagnetic radiation. It reveals the composition and properties of substances by measuring a specific spectrum.
The Science Behind Spectrometry
Spectrometry operates on the principle that different substances interact with electromagnetic radiation in unique ways. When radiation passes through a sample, atoms and molecules can absorb specific wavelengths. This absorption occurs as electrons jump from a lower energy level to a higher one.
The specific wavelengths absorbed depend on the energy differences between electron orbits in atoms or the rotational and vibrational states of molecules. This creates a distinct “absorption spectrum” for each substance, acting like a chemical fingerprint. A detector measures the light passing through the sample, identifying absorbed wavelengths by comparing it to the original source.
Conversely, emission spectrometry involves exciting a sample, causing its atoms or molecules to release energy. This excitation can happen through various means, such as heat or an electrical current. As excited electrons fall back to lower energy levels, they emit photons at specific wavelengths.
The emitted light forms an “emission spectrum,” unique to the substance. By analyzing these specific emitted wavelengths and their intensities, scientists determine the elemental or molecular composition of the sample. Both absorption and emission processes provide insights into the atomic and molecular structure of materials.
Common Spectrometric Techniques
Absorption spectroscopy measures how much light a sample absorbs across different wavelengths. Ultraviolet-Visible (UV-Vis) spectroscopy, for instance, measures the absorption of ultraviolet and visible light by molecules, providing information about electronic transitions. Infrared (IR) spectroscopy measures how molecules absorb infrared radiation, which causes molecular vibrations and helps identify functional groups within organic compounds.
Emission spectroscopy analyzes the light emitted by an energized sample. Atomic emission spectroscopy (AES) examines the light emitted by atoms in a sample, often used to determine elemental composition. Fluorescence spectroscopy occurs when a substance absorbs light and then re-emits it at a longer wavelength, useful for detecting trace substances and studying biological molecules due to its sensitivity.
Mass spectrometry identifies substances based on their mass-to-charge ratio, differing from light-based techniques. A sample is converted into ions, then separated by mass and electrical charge. These separated ions are detected, and the resulting signals form a mass spectrum that provides information about the molecular weight and structure of the compounds present.
Where Spectrometry is Used
Spectrometry has widespread applications, including environmental monitoring. Environmental scientists use visible and ultraviolet spectroscopic methods to detect pollutants in air, water, and soil. Techniques like mass spectrometry and atomic absorption spectroscopy help identify contaminants such as metals in water or particulate matter in air.
In food safety and quality, spectrometry helps ensure the integrity of food products. It identifies contaminants like heavy metals or organic poisons, even at very low concentrations, thereby helping to maintain a safe food supply. Spectrometric methods are also used to authenticate food products and analyze their nutritional content.
Medicine and healthcare benefit from spectrometric methods, which aid in diagnosing diseases and analyzing biological samples. For example, atomic absorption spectrometers can detect and quantify toxic metals in a patient’s blood or urine. The pharmaceutical industry also relies on spectrometry for quality control and purity testing, ensuring medications are safe and effective.
Forensic science utilizes spectrometry for analyzing evidence found at crime scenes. Investigators employ these techniques to identify drugs, analyze fibers, or examine paint samples. By comparing the spectra of crime scene materials to reference spectra, forensic scientists determine their composition and origin.
Spectrometry extends to astronomy, analyzing the composition of stars and distant galaxies. By studying the light emitted from celestial bodies, scientists determine their chemical makeup, temperature, and movement. This helps astronomers understand what stars and planets are made of, even millions of light-years away.