OR
It is the measurement of electromagnetic radiation (EMR) absorbed or emitted when the molecule or cons are atoms of a sample move from one energy state to another state .
🔶Principle of Spectroscopy
• The Principle of spectroscopy is based on the measurement of the spectrum of a sample containing atoms / molecules.
Spectrum is a graph of intensity of absorbed or emitted radiation by sample versus frequency or wavelength .
• Spectrometer is an instrument design to measure the Spectrum of a compound.
🔶 Theory
The theory of UV spectroscopy is based on the absorption of ultraviolet (UV) light by molecules, causing electronic transitions. When UV light passes through a sample, the molecules absorb specific wavelengths, exciting electrons from a lower-energy ground state to a higher-energy excited state.
The amount of light absorbed at different wavelengths is measured, producing a spectrum. This spectrum provides information about the molecular structure, including conjugation and functional groups. The absorption follows Beer-Lambert’s law, relating absorbance to the concentration of the absorbing species.
Gamma Rays <0.001 nm
X-rays <0.01-10nm
U.V 200-400nm
Visible light 400-800 nm
Infra Red 0.8-200 µm
Microwaves 0.01-1m
Radio waves 1-107m
This is completely based on Beer-Lambert Law.
Beer’s law :
Beer’s Law states that the amount of light absorbed by a medium is directly proportional to the concentration of the absorbing species in the medium and the path length of the light through it.
Lambert’ s Law :
Lambert’s Law focuses on the path length and states that:
“Equal thicknesses of the same medium absorb the same proportion of the incident light.”
🔶 Application
1. Qualitative and Quantitative Analysis: Identifies and determines the concentration of compounds, especially those with conjugated systems or aromatic rings, using the Beer-Lambert law.
2. Detection of Impurities: Identifies impurities in samples by comparing the UV spectra of the test sample with a standard.
3. Structure Elucidation: Analyzes functional groups, unsaturation, and conjugation in organic compounds through characteristic absorption bands.
