2. Contents
Introduction
Principle
Choice of Method
Factors Responsible for producing uniform Turbidity
Factors Responsible for Intensity of Scattered Radiation
Effect of Concentration and Wavelength on scattering
Instrumentation
Applications
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3. Introduction
Nephlometry and Turbidometry methods depend on the scattering of light by particles
suspended in a liquid.
The suspended particles have refractive index different from that of the medium.
Nephlometry is measurement of scattered light as a function of concentration of
suspended particles (less than, approximately 100mg/litre)
Turbidometry is measurement of transmitted light as a function of concentration of
suspended particles (more than, 100mg/litre)
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4. Principle
Nephlometry: At low concentration of a suspension there is
uniform scattering of particle. Hence the intensity of scattered
light is directly proportion to the concentration.
The intensity of scattered light is normally measured at 90o
Turbidimetry: At high concentration of a suspension scattering
is not uniform and light is scattered in all direction. Hence the
intensity of transmitted light is measured at 180o
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5. Choice of Method
Nephlometry and Turbidometry depends on the concentration of
suspension
The Concentration of suspension is less, scattering of light is less and
can be accurately measured at 90o.
This makes Nephlometry as the choice in low concentrated suspension.
The Concentration of suspension is more, scattering is also more.
Only transmitted light can be measured at 180o.
This makes Turbidometry as the choice in high concentrated suspension
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6. Factors Responsible for producing uniform
Turbidity
Uniform turbidity of suspension
Manner, order and rate of mixing
Agitation of suspension
Temp. affects solubility of substance and viscosity of medium.
Presence and absence of inert electrolyte
Conc. Of solution mixed to get a suspension
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7. Factors Responsible for Intensity of Scattered
Radiation
No of suspended particle (Con.c)
Size and shape of particle (= or greater than wavelength of light)
Wavelength of radiation not to absorp. Only scattering
Different ref.index of particles and medium
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8. Effect of Concentration and Wavelength on
scattering
Concentration
The intensity of transmitted light is expressed using an equation
P =Power of transmitted light
Po = power of incident beam
T = Turbidity co-efficient
B = Path length
Wavelength
It is expressed by the following equation
T = Turbidity, S = Constant for a given system
= Wavelength. t = size of particle
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9. Instrumentation
Source of Light
Tungsten Lamp & Mercury arc
Filter and Monochromators
Tubidimeter blue filter or 530 nm is used
Sample cells
Detectors
Photovoltaic cell
Photo tube
Photomultiplier
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