Analytical methods Chapter 5
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What is Spectrophotometric measurement?
It is a measurement of light intensity in a narrower wavelength
What is Photometric measurement?
It is a measurement of light intensity without consideration of its wavelength
Is described as photons of energy traveling in waves
Electromagnetic radiation
What is the formula of the Beer’s law?
Concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light
What is the use of Light source?
Incident light for the system
What are the common source of light used near infrared regions?
Incandescent tungsten and Tungsten light bulb
What are the alternatives used for UV spectrum?
Deuterium discharge lamp and mercury arc lamp
What is the use of Entrace slit?
It minimizes the unwanted straylight
What is Straylight?
It is a wavelength outside the band which can affect the measurement and cause absorbance error
What is the use of monochromator?
It isolates specific or individual wavelength of light
Kinds of monochromator
Prisms, Diffraction gratings and Interference Filters
The principle of prism
A narrow beam of light focused on a prism is refracted as it enters the more dense glass
Most commonly used monochromator that consists of many parallel grooves
Diffraction gratings
Principle of constructive interference
Light waves enter one side of the filter and are refracted at the 2nd surface
What is the use of Exit Slit?
It controls the width of the light beam or band pass
The narrower the light beam
the greater the resolution
sample cell/ absorption cell/ analytical cell
cuvet
kinds of cuvet and some definition
Alumina Silica glass- simple/ older Quartz/ Plastic- used for UV spectrum Borosilicate glass- can stand increase temperature Soft glass- Common glass
scatter light and should be discarded
scratches
Produces etching and dissolves glass
Alkaline solutions
What is a Photodetector?
It converts Light energy to Photoelectric Energy
Kinds of Photodetectors:
Photocell, Phototube and Photomultiplier tube
Requires external voltage and it gives off electron when light energy strikes it
Phototube
Simplest detector and no external voltage
Photocell