Ultra-violet spectroscopy/Spectrometry
Ultraviolet/Visible absorption spectroscopy is a measurement of attenuated beam of light after passing through a sample or after reflecting from a sample surface.
Basic Principle: Valence shell electronic transition
Application of UV-Spectroscopy:
- Detection of functional group.
- Detection of impurities.
- Qualitative analysis and Quantitative analysis.
- Single compound without chromophore.
- Identify drugs with chromophoric reagent.
- To identify the conjugated compounds.
Monochromator:
A wavelength selector that uses diffraction grating or prism and allows continuous variation of nominal wavelength.
Filter:
A wavelength selector that uses either absorption and destructive interference to control range of selected wavelength.
Absorption filter: Narrow effective bandwidth 30 to 250 nm and maximum throughput 10%
Interference filter: Narrow effective bandwidth 10 to 20 nm and maximum throughput 40%
Stray light:
Stray light is a light in a optical system, which not intended in the design of instrument/spectroscopy.
In short, it is a unwanted light present in the optical system.
This problem is overcome by using double monochromators in the instrumentation.
Chromophore:
Chromophore is part of a molecule or a structure, which is responsible for colour of the molecule or compound. The colour is obtained by absorbing one of the visible wavelength and reflecting back the remaining ones.
Auxochrome:
An auxochrome is a functional group of atoms attached to the chromophore which modifies the ability of the chromophore to absorb light, altering the wavelength or intensity of the absorption.
List of detectors and principle:
Detector
|
Composition
|
Principle
|
Bolometer
|
Pt strip in
evacuated vessel
|
Resistance change
|
Thermocouple and
Thermophile
|
Two dissimilar metals.
Ex: Bismuth and Antimony
|
Voltage or EMF change at junction
|
Goley Cell
|
Xenon gas
|
Membrane
displacement or expansion of gas
|
Pyroelectric
|
Triglycerine sulphate used as a
medium
|
Electric polarization producing
current.
|
Thermister
|
Oxide of Co, Mg, Ni
|
Resistance change
|
