What is UV Spectroscopy?
Spectroscopy refers to the measurement as well as study of electromagnetic radiation consumed or emitted as molecules, atoms, or ions in a sample shift from one energy level to another. In UV spectroscopy, a kind of absorption spectroscopy, a molecule collects light in the ultra-violet region (200–400 nm), which causes the electrons to be stimulated to an elevated energy state.
Principle of UV Spectroscopy
- Basically, spectroscopy deals with how light and matter interact.
- The amount of energy possessed by atoms or molecules. increases when light is absorbed by matter.
- Absorption of UV light results in the stimulation of electrons from their ground state to a higher energy state.
- By absorbing UV light, molecules having n-or-electrons may stimulate these electrons to elevated anti-bonding orbitals.
- The greater the electron’s ability to absorb longer wavelengths of light, the more quickly it may be energised. The four kinds of transitions (π–π*, n–π*, σ–σ*, and n–σ*), may be arranged in the following order: σ-σ* > n-σ* > π-π* > n-π*
- A chemical substance’s ability to absorb UV light results in a distinctive spectrum that makes it easier to identify the component.
Instrumentation or Parts of UV Spectroscopy
- Tungsten filament lamps as well as hydrogen-deuterium lamps were also the most common and suitable light sources since they emit light over the whole UV spectrum.
- Whenever the performance of Hydrogen-Deuterium lamps is less than 375 nm, tungsten filament lamps release an excess of red radiation, especially radiation with a wavelength of 375 nm.
- Prisms and slits are the most common components found in monochromators.
- Double beam spectrophotometers make up the majority of the available models.
- Rotating prisms are used to spread the radiation that the main source emits.
- The slits then choose from among the numerous light source wavelengths that are separated by the prism, such that when the prism rotates, a sequence of wavelengths with steadily increasing intensities travels through the perforations for purposes of recording.
- Using a second prism, the monochromatic beam selected via the slit is divided into two beams.
Sample and reference cells
- The sample solution is transmitted via one of the two beams, whereas the reference solution is supplied through the other beam.
- The cells contain both the sample and the standard solution.
- These cells are composed of quartz or silica crystals. Glass cannot be utilised for the cells because it also absorbs UV rays.
- Typically, the UV spectroscopy detector consists of two photocells.
- The sample cell’s beam is picked up by one of the photocells, while the reference cell’s beam is picked up by the second detector.
- The radiation beam from the reference cell has a greater energy level than the beam from the sample cell. As a consequence, the photocells generate alternating or pulsating currents.
- The amplifier accepts the photocells’ generated alternating current.
- The amplifier is coupled to a small servo meter.
- Since the power generated by photocells is often quite weak, the major purpose of the amplifier is to multiply the signals such that they are readable.
- Typically, an amplifier is coupled to a pen recorder that is connected to a computer.
- The computer generates the spectrum of the chosen molecule and records all the produced data.
Applications of UV Spectroscopy
Detection of Impurities
- This is among the most effective methods for identifying contaminants in organic compounds.
- Due to the sample’s impurities, additional peaks may be seen, and they can be compared to the characteristics of a typical raw material.
- Additionally, the pollutants may be determined by analysing the absorbency at a certain wavelength.
Structure elucidation of organic compounds
It helps to clarify the structure of organic compounds by identifying heteroatoms and determining whether unsaturation is present or not.
- Utilizing UV absorption spectroscopy, substances that collect UV light may be quantified.
- When judging a product’s quality, UV absorption spectroscopy may be used to characterise the different kinds of UV-absorbing compounds. Identification is achieved by comparing the absorbed spectrum to the spectra of recognised compounds.
- This approach is utilised to evaluate whether or not a chemical has a functional group. The absence of a spectrum at a certain wavelength is considered evidence that a particular category does not exist.
- UV spectroscopy may similarly be utilised to examine the kinetics of a process. The reaction cell is subjected to ultraviolet (UV) light, which causes changes in absorbance that may be seen.
- Many medications are either available as raw materials or as finished products. They may be tested by preparing an appropriate drug solution in a solvent and detecting the absorbance at a particular wavelength.
- By creating the appropriate derivatives of these chemicals, it is possible to spectrophotometrically estimate the molecular weights of various substances.
- A UV spectrophotometer may function as an HPLC detector.