How Does Spectroscopy Function?
Spectroscopy is a broad term that encompasses a wide range of different techniques used to observe how matter interacts with electromagnetic radiation. Techniques are categorized by the region of the spectrum they operate in or the type of interaction observed.
The analysis of a sample’s absorption spectral lines tells us what types of bonds are present in the molecule. This is useful in organic chemistry and in quantifying the concentration of protein or DNA in solution.
Absorption spectroscopy is one of the main techniques used in chemical analysis. It involves directing electromagnetic radiation at a sample and measuring the intensity of the radiation that is absorbed by the material. The resulting spectrum is then recorded and analyzed. This technique is widely used in chemistry, physics, and biology. It is especially useful for identifying trace metals. It has applications in drinking water, mining and mineralogy, oceanographic studies, soils, pharmaceuticals, foods, toys, and forensic investigations.
The absorption spectra are classified according to the type of quantum mechanical change that is induced in the atom or molecule. The lines may be a result of rotational, vibrational or electronic transitions. The width of the line is also influenced by the environment of the sample. For example, liquids and solids tend to have wider lines than gases. The width can also be influenced by the sensitivity of the spectrometer used to record the spectrum. Moreover, the spectrometer has its own inherent limit on how narrow of a line it can resolve.
Emission spectroscopy uses light to reveal the chemical composition of a sample. It involves illuminating the sample with electromagnetic radiation, which then causes atoms to emit energy in a particular wavelength. This energy is then detected and measured, providing information about the sample’s molecular composition.
Scientists can use spectroscopy to determine the elemental makeup of a sample or the concentration of a particular ingredient in a pharmaceutical drug. They can also discover a sample’s temperature, the speed at which it moves through a medium (which is important for astronomy), and even its density.
Each type of atom or molecule interacts with electromagnetic radiation in a different way. This is why each color of a spectrum contains unique information about the sample it is analyzing. The information that is obtained from a given sample can then be used to make better scientific decisions.
In Raman spectroscopy, inelastically scattered light is observed when a molecule makes a vibrational transition from its lower initial state to a higher final vibrational state. The energy difference between the incident and scattered frequencies is related to the shift in the molecular polarizability of the normal coordinates, which reveals the vibrational modes of the molecule.
The resulting vibrational spectrum of the sample includes not only the characteristic peaks of the molecule, but also hot bands (excitations of multiple vibrational states) and overtones (excitation of two or more quanta of the same vibrational mode). The intensity of a Raman peak is proportional to concentration.
HORIBA Scientific is the successor to several of the major innovators in Raman instrumentation including Spex Industries, Coderg/Lirinord/Dilor and Jobin Yvon. We offer a wide selection of fully integrated Raman systems for samples in solids, powders, slurries and liquids. We are also able to provide solutions for Raman measurement of gases when the concentration of molecules is sufficiently high.
Fluorescence spectroscopy allows investigators to probe the intracellular distribution of specific macromolecules in time-resolved measurements. This technique is often used to monitor protein kinetics, membrane integrity, enzymatic reaction rates, and other intracellular phenomena. Unlike X-rays, which cannot penetrate the cell wall, fluorescent techniques can visualize cellular structures and reveal the location of specific molecules.
Once a molecule absorbs a photon it remains in an excited singlet state for a period of time called the fluorescence lifetime before reverting to its ground state and emitting a photon with less energy (fluorescence). This process can be disrupted by processes that do not involve emission of light, such as intersystem crossing to the triplet state or the transfer of energy from one molecule to another.
The probability of fluorescence emission is governed by the extinction coefficient and intrinsic lifetime of the molecule. Those chromophores with high extinction coefficients and long intrinsic lifetimes are more likely to fluoresce than those with low extinction coefficients and short intrinsic lifetimes.