Nephelometry and turbidimetry

NEPHELOMETRY AND
TURBIDIMETRY
By
M Asif Shaheen

NEPHELOMETRY AND
TURBIDIMETRY
INTRODUCTION:
When electromagnetic radiation (light)
strikes on a particle in solution, some of the light
will be absorbed by the particle, some will be
transmitted through the solution and some of the
light will be scattered or reflected. The amount of
light scattered is proportional to the concentration
of insoluble particle.

NEPHELOMETRY AND
TURBIDIMETRY
INTRODUCTION:
• The amount of light scattered is proportional to
the concentration of insoluble particle. We will
focus on the concept of light scatter
• Scattered light may be measured by
Turbidimetry
Nephelometr

visible light
4
Read Out
Device
Turbidimeter
Filter
Sample Cell
Photocell Detector

 Light Scattering Phenomenon:
 The blue color of the sky and the red color of
the sun at sunset result from scattering of light
of small dust particles, H2O molecules and
other gases in the atmosphere.
 The efficiency with which light is scattered
depends on its wavelength, λ.
 The sky is blue because violet and blue light
are scattered to a greater extent than other
longer wavelengths.

THEORY
 Turbidimetry deals with measurement of
Intensity of transmitted light .
 Nephelometry deals with measurement of
Intensity of scattered light.
 Turbidometric measurements are made at
180o from the incident light beam.
 In Nephelometry, the intensity of the
scattered light is measured, usually at right
angles to the incident light beam.

Factors affecting on scattering of
light:
 Concentration of particles
 Particle size
 Wavelength
 Distance of observation,
 MW of particles

Concentration of particles :Turbidimetry
 Concentration of particles: At low concentration of
particles for scattering of light Beers Lamberts law
is applicable.
S=Log10
Io/It
S=KtC=-logT
 Turbidance is directly proportional to concentration
 i.e. S α C
 Where ;S = Turbidance
 IO= Intensity of incident light
 It=Intensity of transmitted radiation
 T=Turbidance
 C=Concentration of solution
 K=constant depend on linearity of light

Concentration of particles :Nephelometry
 In Nephelometry an equation that describe
the relation between the intensity of
scattered radiation , intensity of incident
radiation , and concentration of particles
Is= Ks x IO x C
 Where ;
 IO= Intensity of incident light
 Is=Intensity of scattered radiation
 Ks= It is constant which depend on
suspended particle and suspension medium.
 C=Concentration of solution

Particle Size
 The fraction of light scattered at any angle
depends upon size and shape of particles.
 The amount of scattering (S) α proportional to
square of effective radius of the particle.
 To control the particle size and shape, sample
solutions and standards must be prepared
under identical conditions.
 Following care must be taken:
i) Concentrations of two ions forming ppt.
ii) Ratio of concentration of the solutions.
iii) Order of mixing of ppt.
iv) Temperature at which suspension is prepared.

 Smaller particle (Symmetrically scattering)
 Large particles (Unsymmetrical scattering)
 Larger particles (Unsymmetrical scattering)
1/
4
Particle size smaller 1/10 of incident light
Particle size large 1/4of
incident light

Wavelength
 The intensity of scattered radiation depends
upon wavelength of the incident light.
 Shorter wavelength are scattered to greater
extent than the longer one.
 Wavelength of light is chosen in such a way
that analyte solution does not absorbs
strongly.
 Turbimetric & Nephelometric measurements
are carried using white light.

Molecular Weight
• Direct relationship exist

Distance of Observation
• Light scattering decrease by the distance (r)2
from the light scattering particles to the
detector
S 1/ ∞ r2

Instrumentation:
The instrument called as Turbidimeter
and Nephelometer.
The Basic components of Instruments
are
Radiation
source
Sample
cell
Detector Read out
device

Instrumentation
• Radiation source :Ordinary tungston filament
lamp or mercury arc lamp can be used as
source of radiation.
• Sample cell: The cells made from glass or
plastic are used for study. Rectangular cell
are used in Turbidimeter and Semi
octagonal sample cell are used in
Nephelometer .

Sample Cell in Turbidimeter
IO
It

Sample Cell in Nephelometer
IO It
Is 45o
Is 90oIs 135o

• Detector: Photocell can be used as detector

visible light
23
Read Out
Device
Turbidimeter
Filter
Sample Cell
Photocell Detector

CHOICE OF THE METHOD
 Choice Of The Method depends upon the
amount of light scattered by
suspended particles present in solution.
 TURBIDIMETRY - high concentrated
suspensions.
 NEPHELOMETRY - low concentrated
suspensions - more accurate results

Limitations
• Antigen excess
• Matrix effect

Nephelometry and turbidimetry

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Nephelometry and turbidimetry