Study Set Content:
Light Source → spectrometer
■_____ – if the object does not absorb the energy, it is going to transmit the energy from the light source towards the instrument
Transmittance
Light Source → Light source/towards other direction
■ _____ – it will just bounce back the energy towards the other direction or going back to the light source
Reflectance
refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region
UV-Vis or Ultraviolet Visible spectroscopy
a quantitative technique used to measure how much a chemical substance absorbs light
UV-Vis or Ultraviolet Visible spectroscopy
It is an analytical technique that measures the amount of discrete wavelengths of UV or visible light that are absorbed by or transmitted through a sample in comparison to a reference or blank sample.
UV-Vis or Ultraviolet Visible spectroscopy:
This technique can be used for multiple sample types including
iquids, solids, thin-films and glass.
UV-Vis or Ultraviolet Visible spectroscopy a widely used technique in many areas of science ranging from bacterial (), drug () and nucleic acid ()and quantitation, to () in the beverage industry and chemical research.
culturing, identification, culturing, quality control
An easy-to-use, cheap and robust method offering good precision for making quantitative measurements of drugs in formulations.
STRENGTH
Only moderately selective. The selectivity of the method depends on the chromophore of the individual drugs, e.g a coloured drug with an extended chromophore is more distinctive than a drug with a simple benzene ring chromophore.
LIMITATIONS
Routine method for determining some of the physico-chemical properties of drugs, which need to be known for the purposes of formulation
STRENGTH
Some of the problems of the basic method can be solved by the use of derivative spectra
STRENGTH
Not readily applicable to the analysis of mixtures
LIMITATIONS
PRINCIPLE OF UV-VIS
•
Radiation in the wavelength range _____ is passed through a solution of a compound
200–700 nm
The electrons in the bonds within the molecule become excited so that they occupy a_____ and, in the process, absorb some of the energy passing through the solution.
higher quantum state
The more loosely held the electrons are within the bonds of the molecule, the _____ (lower the energy) of the radiation absorbed.
longer the wavelength
The absorption of UV/visible radiation occurs through the excitation of electrons within the molecular structure to a
higher energy state.
The easier the electrons get excited, the_____ the wavelength of the light, the compound can absorb
longer
The transition of electrons always occurs from the ground state of low energy _____ (highest occupied molecular orbital) to a higher energy excited state_____ (lowest unoccupied molecular orbital).
HOMO, LUMO
Involves the transfer of electrons between different electronic state - ground state to the excited state
ELECTRONIC TRANSITION
() When UV is absorbed, an electron is raised from the ground state to excited state, loses its vibrational energy, decays to ground state, emitting UV or visible light
When the transition back to the ground state is delayed it results to
Fluorescence phosphorescence.
