1. Uv visible spectroscopy
Construction and working of detectors
This is based on the study of absorption of radiation which usually
ranges from 200 -400nm
The nature of the electrons decides the absorption , these electrons tend to absorb the
energy and we can see a transition from ground state to excited state
Instrumentation:
Suitable source
Lens mirror slit
Monochromator
Sample
Detector
Amplifier and readout device
Detectors :
These are devices which are used to convert light energy into electric energy
The results are been displayed on the read out device at end
It consists of a
Photo multiplier
Barrierlayer cell
Photo tube.
Photo multiplier tube :
This is composed of 2 components photocathodes and dynodes
2. The photocathode has photoemissive surface on which the photons strikes and results
in release of electrons
The electrons are in equal number as that of photons that striked
These electrons again hit the dynodes that results in release of more electrons
it amplifies the electric signal
In case of weak electromagnetic radiation of sample photomultiplier is used in place of
photodiode arrays
The increase in electric signal equals initial electromagnetic radiation in the sample
This is highly sensitized by light radiation
A minimum of 8 to 10 dynodes are arranged with 75 – 100v potential difference s
Barrier layer cell / photovoltaic cell
This detector is made up of iron and coated with a film of semiconductive material
This device works well with intense light sources as it does not exhibits huge signal
enhancement
In this a potential difference is seen between 2 electrodes and this is reason for flow of
current
The 2 electrodes are separated by selenium layer which is semi conducter
Galvanometer is connected flow of current observed it is equal to intensity and
wavelength
Photo tubes / photoemissive tubes
It is used widely as it is More sensitive compared to barrer layer cell
This has a glass tube with photocathode and anode
Photo cathode is coated with cesium / silver
Energy hits photosensitive cathode
Electrons are emitted and reaches anode results in flow of current
3. Reference :
Instrumental method of chemical analysis by gurdeeP R chatwal and sham K. Anand
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