Study Set Content:
Employs a diffraction grating, which disperses light into its spectral components based on the principle of diffraction. By rotating the grating, different wavelengths can be selected.
Grating Monochromator
offer higher spectral resolution and are commonly used in modern UV/VIS spectrometers. They are also the most effective one in converting a polychromatic light to monochromatic light.
Grating monochromators
Utilizes optical filters, such as interference filters or colored glass filters, to selectively transmit certain wavelengths of light while blocking others
Filter Monochromator
are often used in simpler UV/VIS instruments but may have limited spectral bandwidth and resolution compared to prism and grating monochromators.
Filter monochromators
Types of Filters
Glass filters-
Gelatin filters
Inter ferometric filters
Made from pieces of colored glass which transmit limited wavelength range of spectrum. Wide band width 150nm.
Glass filters-
Consist of mixture of dyes placed in gelatin & sandwiched between glass plates. Band width 25nm.
Gelatin filters-
Band width 15nm
Inter ferometric filters
SAMPLE CONTAINER or CUVETTE
Made up of:
- Quartz
- Borosilicate
- Plastic
is transparent in both UV & Visible regions (200-700 nm range).
Only quartz
are suitable for the visible region only.
Glass & Plastic
is not suitable for the UV region because it absorbs UV radiation
Glass
are not used for organic solvents
Plastic Cells
are devices that convert radiant energy into electrical signal.
The transmitted radiation falls on the detector which determines the intensity of radiation absorbed by sample.
DETECTORS
Requirements of an ideal detector:
•
It should give quantitative response.
•
It should have high sensitivity and low noise level.
•
It should have a short response time.
Three common types of Detectors used:
Barrier Layer Cell -
Photodiode arrays
Photomultiplier Tubes
Also called as photovoltaic cell. It consists of flat Cu or Fe electrode on which semiconductors such as selenium is deposited. On the selenium a thin layer of silver or gold is sputtered over the surface.
Barrier Layer Cell
Offers advantages such as high sensitivity, fast response times, and simultaneous measurement at multiple wavelengths.
Photodiode arrays
It is generally used as detector in UV- spectrophotometer. It is the combination of photodiode & electron multiplier. Provide high sensitivity and low noise, making them suitable for low light intensity measurements
Photomultiplier Tubes
These instruments may either be manually operated or automatic recording instruments.
Spectrophotometer
