Spectroscopy Methods
These are the spectroscopic methods that analytical laboratories rely on
When Joseph Fraunhofer, mirror manufacturer, optician and physicist, invented the spectroscope while researching sunlight in 1814, he laid the foundation for one of today’s most important scientific analysis methods. A prism spectroscope helped him to catalog the spectral lines of sunlight. Earlier still, in the 17th century, Isaac Newton had discovered that white light is composed of the spectral colors. How present-day analytical laboratories in industry and research would operate without spectroscopy methods is unimaginable.
Among the many spectroscopy methods used to analyze structures and substances, these are the ones you should know.
Contents
- IR and NIR spectroscopy
- UV/VIS spectroscopy
- Nuclear magnetic resonance spectroscopy (NMR)
- Mass spectrometry (MS)
Spectroscopy, spectrometry, spectrogram and spectrum – the basics in a nutshell
Physical methods that separate radiation according to certain properties, such as wavelength, energy or mass, are called spectroscopy. The radiation is made visible with a spectroscope. The visual evaluation is called spectrogram (usually shortened to “spectrum”). The spectral lines or bands it displays constitute a kind of optical fingerprint of a sample. They help to identify chemical elements by spectroscopy methods, which can be based on either emittance, absorption or fluorescence processes in atoms (atomic spectroscopy). Evaluating the spectrograms also helps to characterize molecules by measuring their properties and drawing conclusions about the rotation, vibration and electron states in a molecule.
Combining the spectroscope with a detector, which measures the intensity of the spectral bands, creates a spectrometer, and the method is called spectrometry.
Spectroscopy methods for analytical laboratories with which you should know about
To determine the composition or state of a sample using spectroscopy methods, a wide variety of radiation types can be used. The most common is electromagnetic spectra, where the electromagnetic waves are separated into their contained individual wavelengths or frequencies. Depending on which spectral range you are focusing, the methods are known as, for example, infrared, UV, X-ray or gamma spectroscopy. Other well-known methods are ultrasound spectroscopy, neutron spectroscopy and mass spectrometry.
IR and NIR spectroscopy
IR spectroscopy uses reference spectra for the quantitative determination of known substances. However, shedding light on the structure of unknown substances is also possible with this spectroscopic method. IR spectroscopy investigates how electromagnetic radiation of the infrared spectral range (wavelengths from 800 nm to 1 mm) interacts with the sample. When IR radiation hits a sample, some frequencies are absorbed while others pass through. Molecules change their rotational and vibrational energy as the radiation is absorbed, so the IR spectrum allows conclusions to be drawn about the structure of the molecules.
Samples can also be examined very quickly by Fourier transform infrared spectroscopy (FT-IR). This method analyzes all wavelengths in a single measurement rather than only one specific wavelength at a time.
Near-infrared spectroscopy (NIR spectroscopy) is another method allowing the rapid examination of substances and substance mixtures. The instruments use light of between 800 and 2,500 nanometers in wavelength, which lies between the visible spectral range (VIS) and the mid-infrared (IR) range. The NIR radiation excites the molecules of the sample into vibration. Information about the molecular composition can then be deduced from the reflected spectra.
The instruments
IR spectroscopy instruments consist of a radiation source and a detector, for example a pyroelectric or Golay detector. To help you choose the right instrument from the many available on the market today, there’s information about all the relevant manufacturers and their products in the world's largest market overview of NIR spectrometers.
UV/VIS Spectroscopy
This spectroscopy method uses electromagnetic waves of the ultraviolet (UV) and visible (VIS) light spectrum. In this range, only the state of the outer electrons, which are furthest away from the atomic nucleus, changes when a sample is irradiated. These molecule bonding electrons are excited to transition, and only light of a certain wavelength is absorbed. The spectrum shows an absorption maximum or band.
Many organic compounds absorb in the UV range, so this fast and precise method is used in many ways, for example to determine the concentration of known substances, to test for purity or to investigate reaction kinetics. For analytical laboratories, UV/VIS spectroscopy is indispensable these days.
The instruments
UV-VIS spectrometers consist of a radiation source (deuterium or tungsten lamp), a monochromator (prism or grating) to select the wavelength for the measurement, and a rotating mirror on which the light beam falls. Alternately, the light beam is directed through a cuvette containing the sample in solution and a cuvette containing a reference solution. A detector connected to a recorder then receives the two light beams.
For a comprehensive selection of instruments, see the world's largest market overview of UV-VIS spectrometers.
Nuclear magnetic resonance spectroscopy (NMR)
NMR spectroscopy is one of the most powerful spectroscopic methods to examine the structure of unknown (usually organic) compounds or to analyze known substances. NMR systems measure how magnetically active atomic species respond to a radiofrequency pulse in a magnetic field. The nuclei most frequently studied are H1 and C13.
Molecules in solution are easy to measure by NMR spectroscopy. The sample is exposed to a homogeneous magnetic field (the main magnetic field) into which radio wave pulses are transmitted using modern measurement techniques, for example PFT NMR spectroscopy (pulsed Fourier transform NMR spectroscopy). The resulting signals reveal the chemical environment of these atoms, and by comparing them with NMR spectra of known reference substances, many compounds can be quickly identified.
Mass spectrometry (MS)
Mass spectrometry is often considered a spectroscopy technique as well because it serves similar purposes in analytical laboratories. However, unlike IR, UV-VIS and NMR spectroscopy, it is not a non-destructive spectroscopy method.
A mass spectrometer identifies molecules and atoms by mass. This instrument makes it possible to fragment inorganic or organic compounds into ions, determine the mass of the individual constituents, and to create a characteristic, fingerprint-like pattern. For this purpose, modern mass spectrometers require an ion source, a mass analyzer and a detector. Find out more about this method by visiting our Focus Topic Mass Spectrometry in our world of specialist topics.
Discover suitable mass spectrometers for almost any application in the world's largest market overview of mass spectrometers.
Conclusion
Spectroscopy methods simplify everyday laboratory routines in industry and research. Atomic elements or molecules can be identified quickly and correctly, and even their structures can be examined. Combining several methods improves such analyses even further. In addition to the methods discussed here, a large number of other spectroscopic methods are used in modern analytical laboratories, such as Raman spectroscopy, electron spin resonance spectroscopy or microwave spectroscopy.
