In the formula for the turbidity measurement from UV-Vis data, it is given that
turbidity=(2.3*A)/L, where A is the absorbance and L is the optical path length. Can anyone tell me why there is a constant 2.3 in this formula? Is it same for all kind of materials?
Thanks in advance.
Keep in mind two things:
1. Lambert Beer law is logarithmic
2. Conversion factor 2.303 allows changing the base of the logarithms.
Dear Mithra.,
In Turbidity measurement you are using UV-Vis Spectrometer I think you are measuring Absorbance @ 420nm
In that UV- Vis you have to calibrate with diff concentration of turbidity standard such as 1, 5, 10, 20…..400 NTU turbidity standard and you will get different absorbance
Then you have to plate a calibration curve by using beers law
That time you will get a Slope value it might be that what you are telling (2.3) that value that will be variable
In optics UV- Vis calibrated with standard filters and they given the standard values
Turbidity standard preparation
• Hexamethylene Tetramine solution: Dissolve 10g hexamethylene tetramine in demineralised water and dilute to 100ml.
• Hydrazine Sulphate Solution: Dissolve 1.00g Hydrazine sulphate (NH2)2H2SO4 in distilled water and dilute to 100ml.
• Turbidity Standard suspension I (Formazin)- In a 100 ml volumetric flask mix 5.0 ml hydrazine sulphate solution with 5 ml haxamethylene tetramine solution. After 24 hour standing at 25± 30C dilute to 100ml with demineralized water and mix well
• Turbidity Standard suspension II (Formazin) -Dilute 10ml turbidity standard suspension I to 100ml with distilled water. The turbidity of this suspension is defined as 40 NTU. Prepare fresh weekly. This suspension may be diluted as required to prepare more dilute turbidity standards.
https://law.resource.org/pub/in/bis/S02/is.3025.10.1984.pdf
The short answer is: 2.3=Ln(10)
In those kind of measurements, what is measured is the light transmitted through the solution (It) with respect to the light transmitted through the pure solvent (Io).
By definition, turbidity=-Ln(It/Io) and absorbance=optical density=-Log(It/Io)
So, there is a conversion factor of Ln(10) between the 2.
(Ln: neperian logarithm; Log: decimal logarithm)
Yes i understood the explanation now. Thanks for all the answers. My basic question was if i find out the absorbance of a material(expressed as a product of optical path length, molar absorption coefficient and concentration), then can i calculate turbidity from the above formula?
Thanks for the time.
Yes, as long as the concentration is not too high: there are limits to the Beer Lambert law.
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