When we talk about UV spectroscopy or UV–visible spectrophotometry, we’re talking about absorption spectroscopy or reflection spectroscopy in the ultraviolet and neighbouring visible parts of the electromagnetic spectrum. This means that it makes use of light that is visible and next to it. The absorption or reflectance of the chemicals involved in the visible spectrum has a direct impact on the apparent colour of the compounds. Electronic transitions occur between atoms and molecules in this region of the electromagnetic spectrum. As a companion technique to fluorescence spectroscopy, absorption spectroscopy examines electron transitions from the excited state to the ground state, whereas fluorescence is concerned with electron transitions from the excited state to the ground state.

A brief description on UV Visible Spectroscopy 

Ultraviolet-visible spectroscopy (UV-VIS spectroscopy) is an analytical technique that analyses the number of discrete wavelengths of ultraviolet or visible light absorbed or transmitted through an object in comparison to a reference or blank object. Depending on the sample composition, this feature may be useful in determining what is in the sample and at what concentration it exists. Because this spectroscopy approach is dependent on the usage of light, let us first analyse some of the characteristics of light itself.

Light has a specific amount of energy that is inversely proportional to the wavelength of the light it emits. The result is that the energy carried by shorter wavelengths of light is greater than that carried by longer wavelengths of light. The promotion of electrons in a substance to a higher energy state, which we can detect as absorption, necessitates the use of a precise quantity of energy. To promote electrons to a higher energy state in a substance, electrons in different bonding environments require a different specific amount of energy than electrons in other bonding contexts. As a result, different wavelengths of light are absorbed by different substances, resulting in varied absorption coefficients. Humans are capable of seeing a spectrum of visible light ranging in wavelength from roughly 380 nm, which we perceive as violet, to approximately 780 nm, which we perceive as red. Ultraviolet light has wavelengths that are shorter than those of visible light, and its wavelengths are around 100 nm. As a result, the wavelength of light may be defined, which can be used in UV-Vis spectroscopy to study or identify distinct compounds by determining the exact wavelengths corresponding to maximal absorption.

Application

• For the quantitative determination of various analytes or samples, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules, ultraviolet/visible spectroscopy (UV/VIS) is commonly used in analytical chemistry. Although spectroscopic analysis is most typically performed on solutions, it can also be performed on solids and gases.
• Analysis of beverages: Another common application of UV-Vis spectroscopy is the identification of specific substances in beverages. In order to be legal, the caffeine concentration must be kept under specified legal limits for which UV light can be used to aid in quantification. Using UV-Vis absorbance, some classes of colourful chemicals, such as anthocyanins (found in blueberries, raspberries, blackberries, and cherries), may be easily detected by matching their known peak absorption wavelengths in wine for quality control, which can be done quickly and efficiently. 
• Bacterial culture: In bacterial culture, ultraviolet-visible spectroscopy (UV-VIS) is frequently utilised. OD measurements are conducted routinely and fast using a wavelength of 600 nm to estimate the cell concentration and to track growth in order to estimate the cell concentration and to track growth. In most cases, the wavelength of 600 nm is employed and chosen because of the optical qualities of the bacterial culture conditions in which they are produced, and to avoid killing the cells in cases where they are necessary for continuing testing.
• DNA and RNA analysis: One application that is particularly popular is the rapid verification of the purity and concentration of RNA and DNA samples. For downstream applications such as sequencing, it is frequently necessary to check that the DNA or RNA samples have not been contaminated with one another or with protein or chemicals that have been carried over from the isolation procedure during preparation.

Conclusion

UV-Vis spectroscopy is also beneficial in some more specialised research because of its qualitative properties. Changes in the wavelength corresponding to the peak absorbance may be tracked, which is valuable for investigating specific structural protein changes and determining the composition of batteries, for example. Increased sensitivity to shifts in peak absorbance wavelengths can also be relevant in more current applications, such as the characterisation of ultra-small nanoparticles and other nanomaterials. The possibilities for this method are numerous and appear to be virtually limitless.

This technique is also applicable in a variety of other sectors. It is useful to monitor transformer oil, for example, in order to ensure that electric power is delivered in a safe and reliable fashion. The ability to measure haemoglobin absorbance in order to calculate haemoglobin concentrations may be useful in cancer research. Using UV-Vis spectroscopy in wastewater treatment, kinetic and monitoring studies can be conducted to ensure that specific dyes or dye by-products have been effectively eliminated from the wastewater by comparing their spectra over time. It is also extremely useful in the investigation of food authenticity and the monitoring of air quality.