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

Contents 3.3 Turbidimetry and Nephelometry (04L) 3.3.1 Scattering of Radiations. 3.3.2 Factors affecting scattering of Radiation: Concentration, particle size, wavelength, refractive index. 3.3.3 Instrumentation and Applications of Turbidimetry and Nephelometry .

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.

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.

Turbidimetry Nephelometry

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: Concentrations of two ions forming ppt. Ratio of concentration of the solutions. Order of mixing of ppt. Temperature at which suspension is prepared.

Nephelometry Turbidimetry

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

Molecular Weight

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 It IO

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

Detector: Photocell can be used as detector

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

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

Nephelometer visible light Light Trap Photocell Detector Sample Cell Graduated Disc Collimating Lens Light Trap visible light Photocell Detector Sample Cell Read Out Device

Turbidimeter Turbidimetry Photocell as detector Radiation Source Collimating Lens

NEPHELOMETER

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

APPLICATIONS Quantitative analysis of Inorganic species Air and water pollution Turbidimetric titrations Phase titrations Determination of Molecular weight

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

2. Air and water pollution . 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. Ex. Water treatment plants, sewage work, refineries, paper industry . Determination of Phosphorus at trace levels(1 parts in more than 300 million part) by precipitating it by strchine –molybdate reagent. Determination of trace levels of ammonia: Ammonia can be detected at concentration of 1 parts in 160 million by using Nessler’s reagent

3.Turbidimetric titrations 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 . b Curve I is an Ideal curve Curve II and III are not because of improper stirring. I II III

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.

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 =1/M where H is constant for given polymer. C is concentration of polymer in g/cm3. Hc T

Concentration of Polymer Hc/T 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 1/M Concentration of Polymer

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.

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