James Everitt blogs on UV/Visible Spectroscopy

UV/Visible spectroscopy relies on the interaction of molecules with electromagnetic radiation mainly in the ultra-violet and visible parts of the spectrum. This electromagnetic radiation according to quantum theory acts as both a particle and wave, known as wave-particle duality, it is this particle nature that allows electromagnetic radiation to interact with electrons and allow us to observe them.
All electromagnetic radiation travels at the same speed (the speed of light) this speed is the product of the wavelength and frequency of that radiation. As stated previously light can behave as a quantised particle where its energy is directly proportional to the frequency of the radiation.

UV/Visible spectroscopy measures the absorbance of a molecule to determine what that molecule is. This is calculated using Beer’s Law which can be turned into an equation:

 

The molar absorption constant at a certain wavelength is what allows us to determine what the molecule is, because it is pre-recorded when the nature of the sample is known. However, first absorption must be calculated which is done by measuring the percentage intensity of the light after it has passed through the sample:

 

Using this equation we can calculate the molar absorption constant and therefore find the molecule.