Nephelometry and Turbidimetry TYBSC

1. Satish Pradhan
Dnyanasadhana College, Thane.
Department of Chemistry
T.Y.B.Sc. Analytical Chemistry
Paper-IV Sem-V
NEPHELOMETRY AND TURBIDIMETRY
1

2. Turbidimetry and
Nephelometry (04 L)
3.3.1 Introduction and
Principle
3.3.2 Factors affecting
scattering of Radiation:
Concentration, particle size,
wavelength, refractive index
3.3.3 Instrumentation and
Applications

3. 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.

4. 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.

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

6. Turbidimetry
Nephelometry

7. Factors affecting
on scattering of
light
Concentration of
particles
Particle size
Wavelength
Distance
of observation,
MW of particles

8. • Concentration of particles: At low concentration of particles for
scattering of light Beers Lamberts law is applicable.
• S=Log10
Io/It
S=KtC=-logT
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
Turbidance is directly proportional to concentration
• i.e. S α C
Concentration of particles :Turbidimetry

9. • 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
Concentration of particles :Nephelometry

10. 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
to control Particle Size
Concentrations of two ions
forming ppt.
Ratio of concentration of the
solutions.
Order of mixing of ppt.
Temperature at which
suspension is prepared.

11. Turbidimetry
Nephel
ometry

12.  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

13. Wavelength
The intensity of scattered radiation depends
upon wavelength of the incident light.
Shorter wavelength are scattered to greater
extent than the longer one.
Turbidity coefficient depends on wavelength
of incident light.
K=S xλ-1 (where s= constant for system)
Wavelength of light is chosen in such a way
that analyte solution does not absorbs
strongly.
Turbimetric & Nephelometric
measurements are carried using white light.

14. 1.Radiation
source
2.Sample
cell
3.Detector
4. Read out
device
Instrumentation
The Instrument called as Turbidimeter and
Nephelometer.
The Basic components of Instruments are

15. 1.Radiation
source
Ordinary tungsten
filament lamp or
mercury arc lamp
can be used as source
of radiation.
2.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 .

16. IO
It
Sample Cell in Turbidimeter

17. IO It
Is 45o
Is 90o
Is 135o
Sample Cell in Nephelometer

18. • Detector: Photocell can be used as detector

19. visible light
19
Read Out
Device
Filter
Sample Cell
Photocell Detector
Turbidimeter

20. visible light
20
Read Out
Device
Filter
Sample Cell
Photocell Detector
Turbidimeter

21. visible light
21
Light
Trap
Read Out Device
Sample Cell
Photocell Detector
D
E
T
C
T
O
R
Collimating Lens
Graduated Disc
Nephelometer

22. CHOICE OF
THE METHOD
TURBIDIMETRY -
high concentrated
suspensions.
NEPHELOMETRY -
low concentrated
suspensions - more
accurate results

23. APPLICATIONS
1
• Quantitative analysis of Inorganic species
2
• Air and water pollution
3
• Turbidimetric titrations
4
• Phase titrations
5
• Determination of Molecular weight

24. 1. Quantitative analysis of Inorganic species
• In gravimetric analysis certain ppt.particles are
very small in size so they are difficult to filter .
• Quantitative analysis of such ppt. compound can
be carried out by calibration curve method.
Examples
• SO4-2 as BaSO4
.
• CO3
-2 as BaCO3
.
• Cl as AgCl
• Ca+2 as Calcium oxalate

25. 2. Air and water pollution
1
• Air and water pollution Air Pollution: particulate matter in
air ,dust, smoke can be monitored by the Nephelometry and
Turbidimetry.
• Water Pollution: Turbidity of water can be monitored
continuously by Nephelometry and Turbidimetry.
Examples
• Water treatment plants, sewage work, refineries, paper industry
2
• Determination of Phosphorus at trace levels(1 parts in more
than 300 million part) by precipitating it by strchine –
molybdate reagent.
3
• Determination of trace levels of ammonia: Ammonia can be
detected at concentration of 1 parts in 160 million by using
Nessler’s reagent

26. 3.Turbidimetric titrations
•
Curve I is an Ideal curve
Curve II and III are not
because of improper
stirring.
II I
III
• The Turbidimetric titrations are those in which turbidance
is used to locate end point using a titrant that gives
precipitate .
• Ex. Titration of Ba+2 against H2SO4 solutions of
concentration up to 10-5 to 10-6 M can be determined

27. 4.Phase titrations
• The Turbidimetry can be used for titration
of two liquids with third liquid which is
miscible with only one of two liquids in
mixture.
• Ex. Mix. Of Ethanol and benzene , water is
miscible with ethanol but not with benzene.
• Water pyridine mixture titrated with CHCl3.

28. 5.Determination of Molecular weight
• Molecular wt. of polymers such
as polyvinyl alcohol can be
determined.
• Following relationship holds
between turbidity and Mol.wt.
• Lim HC/T =1/M where H is
constant for given polymer.
• C is concentration of polymer
in g/cm3.

29. Turbidity of solution is
measured at different
concentration using
suitable solvent.
The plot Hc/T is extra
plotted to zero
concentration to get
intercept equal to
1/M
Concentration of Polymer
Hc/T
1/M

30. 6. Biochemical analysis
• Turbidimetry can be used
to measure the growth of
bacteria in a liquid
nutrient medium.
• It is also used to
determine the amount of
amino acids, vitamins and
antibiotics.

31. •All the best