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INTRODUCTION When electromagnetic radiation (light) strikes 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. We will focus on the concept of light scatter

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THEORY Scattered light may be measured by Turbidimetry Nephelometry In turbidimetry, the intensity of light transmitted through the medium, the unscattered light, is measured.

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Turbidometric measurements are made at 180o from the incident light beam. In Nephelometry, the intensity of the scattered light is measured, usually, but not necessarily, at right angles to the incident light beam.

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The two techniques differs only in the manner of measuring the scattered radiation.

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Turbidity can be measured on most routine analysers by a spectrophotometer (absorbed light) Reduced sensitivity and precision. Extent of light scattering increases as wavelength increases The intensity of scattered light is normally measured by Nephelometer.

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Light scattering is the physical phenomenon resulting from the interaction of light with a particles in solution. Dependent on : Particle size Wavelength Distance of observation, Concentration of particles MW of particles

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Tyndall Effect Scattering of light- by particles in a colloid or suspension. the longer-wavelength light is more transmitted while the shorter-wavelength light is more reflected via scattering.

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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, ?. The sky is blue because violet and blue light are scattered to a greater extent than other longer wavelengths.

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NEPHELOMETRY v concentration, uniform scattering, intensity of scatted light proportional to conc. measured at 900 TURBIDIMETRY ^ concentration, scattering not uniform, intensity of transmitted light measured at 1800

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Turbidimetry ¦ Colorimetry Measurement of the intensity of light transmitted through a medium, light intensity is decreased. Nephelometry ¦ Fluorimetry Measurement of scattered light at 900

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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

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INSTRUMENTATION The basic instrument contains Light Source:Tungsten lamp, White light - nephelometers Filters - Turbidimeter (blue filter or 530 nm) Nephelometer (visible filter) Sample cells Detectors (photometric)

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CELLS cylindrical cells - flat faces to minimize reflections & multiple scatterings

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FACTORS AFFECTING MEASUREMENTS The amount of radiation removed or deviated from the primary radiation beam depends on the following factors 1.Concentration Turbidimetry: S = log I/Io= kbc T=Transmittance = I/Io S = turbidence due to scattering k = turbidity constant b= path length c = concentration of suspended material

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Nephelometry: Is = Ks Io C Is = scattered intensity Ks= empirical constant Io = Incident intensity c = concentration of suspended material

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2. Effect of Particle Size on Scattering Size and the shape of the particles responsible for the scattering. Because most analytical applications involve the generation of a colloidally dispersed phase in a solution, those variables that influence particle size during precipitation also affect both turbidimetric and nephelometric measurements.

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Turbidimetry-Practical Considerations Selecting ?: Important. It is necessary to avoid radiation that is absorbed by the sample. Sample Preparation Scattering is related to: 1.Concentration of the scattering particles 2.Particle size 3.Particle shape

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APPLICATIONS Analysis of water clarity, conc. of ions Determination of CO2 Determination of inorganic substances Sulphate – barium chloride Ammonia – Nesslers reagent Phosphorus – Strychine molybedate Biochemical Analysis 5. Quantitative Analysis – (ppm level)

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6. Miscellaneous Water treatment plants, sewage work, refineries, paper industry 7. Atmospheric pollution smokes & fogs 8. Determination of mole. Wt of high polymers 9. Phase titration NEPHLOTURBIDIMETER Two detectors

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