To measure water turbidity we have to compare nephelometric 900 scattered intensity with that of Formazine standard solution but we don't know about the particle distribution suspended in water, natural water may contain particles of different sizes and shapes. Does measuring scattering at 900 makes the reading independent of particle size and shape? Is there any relation which relates water turbidity with the scattered intensity and wavelength used?
There is a simple formula relating turbidity (measured by transmittance) to optical properties. Van de Hulst (“Scattering of light by small particles”, Dover, 1957, reprint 1981) describes it as “one of the most useful formulae in the whole domain of Mie theory”.
Unfortunately, nephelometric turbidity (in NTU) is not the same thing. It is measured at 90° scattering angle. In general, the relationship between NTU, particle size and optical properties can only be calculated using Mie theory. However, you can use the simple Rayleigh-Debye formula if the particles are much smaller than the wavelength of the light. I was surprised to find that this calculation shows that as the particle diameter goes up, the NTU reading goes down.
Plug "nephelometeric " into Google search and you should get all the answers you need.
Iftak as you desired the equation is :
Jackson Turbidity Unit ( JTU ) =. Observed Turbidity x Final Dilution Volume / Original Sample Volume.
Laser intensity in nephelometry play an important rôle in particle detection. At low intensity you increase the background, so very small particles are included in this background but you can measure a very concentrate suspension. Each different particles have a specific impact in nephelometry because of form. Nephelometric unit is RNU for relative nephelometric unity
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