UV Spectroscopy or Ultraviolet-visible spectroscopy is an advanced technique based on the absorption of ultraviolet light or visible light by chemical compounds. This technique is widely used to know the absorbance spectra of a compound in solution or as a solid in various fields of science ranging from bacterial culturing, drug identification, and nucleic acid purity checks and quantization, to quality control in the beverage, refinery industry, and chemical research.
The interaction of light with matter at electronic levels can be identified by this UV Spectroscopy or spectrophotometer technique. It identifies the ranges from the vacuum level ultraviolet region (180nm) to the visible region (780nm) wavelength. The UV spectrum shows the wavelength ranges from 180nm to 400nm whereas the visible region ranges from 400nm to 780nm.
This versatile technique is very suitable for qualitative as well as quantitative analysis of various chemicals sample. It is very much used to observe the optical characteristics of chemical compounds and identification of various species properly.
The electronic transition that occurs during the absorption of radiation from the ultraviolet to the visible region is plotted in a graph. This graph shows the various absorptivities on specific levels of radiation known as regions of absorption and the compounds are termed chromophores.
UV Spectroscopy working principle
The working principle of UV Spectroscopy relates to the absorption of UV or visible light by sample compounds, which creates distinct spectra. The sample chemical produces a spectrum when it absorbs the light. The electrons of the sample material undergo excitation and de-excitation states after absorbing light.
When materials absorb UV radiation, the electrons get excited and jump from a ground state to an excited state. The energy difference between the ground state and the excited state of the electron is equal to the amount of UV radiation or visible radiation absorbed by it.
Actually, the π-electrons or nonbonding electrons (n-electrons) of the molecules are responsible to absorb energy in the form of UV radiation to excite these electrons to higher anti-bonding molecular orbital. If the electrons are excited easily, they can absorb longer wavelengths of light.
The sample compound produces a distinct spectrum which helps in the identification of the compound.
UV Spectroscopy instrumentation
The instrumentation of UV Spectroscopy is discussed below:
Light Source: Hydrogen lamps, deuterium lamps, Xenon arc lamps,s and Tungsten halogen lamps are used for getting light in this spectrometry. The wavelengths of Hydrogen & deuterium lamps are 160-380nm. The wavelength of a Xenon arc lamp range is 250-600nm whereas a Tungsten halogen lamp’s wavelength range from 240nm to 2500nm.
Wavelength selector: This spectrometer requires a single wavelength to get proper results. There are two popular wavelength selectors namely Filters and Monochromators. Filters are used to get a specific band of wavelength. Glass filters are generally used in this technique because they can absorb a broad portion of the spectrum (various colors) and transmit other portions as their own color. The filters are generally cheap and the working principle is very simple.
Monochromators: It is an optical device that is used for the selection of a narrow band of a wavelength of light. The monochromator is generally made of quartz or glass and acts like a prism or grating. It is used to scan the spectral data at the UV-visible region. This part consists of a slit, mirror, lens, grating, or prism.
Sample container/cells or cuvettes: This part is made of plastic, borosilicate glass, or quartz material. Quartz is very suitable in both UV & visible regions (200-700nm range). Borosilicate Glass & plastic materials are suitable for the visible region only. The size of the sample container ranges from 0.1-10 cm.
Detectors: This part indicates the various physical phenomenon of the tested sample. There are many types of indicators such as transducers, photodetectors, photographic films, etc. Transducer is mostly used as a detector for converting signals such as light intensity, pH, mass, temperature, etc into electrical signals which are amplified and manipulated. It produces a fast response to low levels of radiant energy.
Advantages of UV Spectroscopy
This popular technique is completely non‑destructive and allows the sample to be reused. It can be measured very quickly by UV-Vis spectroscopic technique. The various part of this instrument can be used easily. The UV-Visible spectrometric technique is not expensive and allows little user training is required.
Limitations of UV-Visible spectrometry
This spectroscopy is not suitable to analyze compounds that do not interact with light in the UV and visible areas of the spectrum. Some inorganic compounds and organic components do not interact with light in the UV and visible areas of the spectrum because of the absence of a high level of electron conjugation.
Applications of UV Spectroscopy
Ultraviolet-visible spectroscopy is used to characterize the nanoparticles. UV Spectroscopy is a suitable technique to determine the composition of the battery. This spectroscopic technique is used to monitor the studies of dyes and dye byproducts. The enzymatic reactions can be known by this spectroscopy. It is very much used as a detector for HPLC. This process is used to examine the characteristics of the polynuclear hydrocarbon. Functional groups can be identified easily by UV spectroscopy. This technique is used in FMCG industries to identify and quantify various components. This non-destructive technique is used for DNA and RNA analysis.
References
1.Weckhuysen, B. M. (2004). Ultraviolet-visible spectroscopy.
2.Power, A. C., Chapman, J., Chandra, S., & Cozzolino, D. (2019). Ultraviolet-visible spectroscopy for food quality analysis. Evaluation technologies for food quality, 91-104.
