Galvanic Applied Sciences USA, Inc.
101 Billerica Ave, Bldg. 5, Suite 104.
North Billerica, MA. 01862
Tel: 978-848-2701
Fax: 978-848-2713
Email: [email protected]
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Context between particle size, measurement method and results
The most common Calibration standard for turbidity is based on formazin liquid.
When using formazin as calibration standard, defined formazin suspensions should display identical
measurement results with both methods: 12° and 90°.
During observation of a real sample, such as filtered beer, the different methods will have different
measurement results. The measurement results of the 90° side scatter method are typically a factor of 3 to
10 times greater than the measurement results of the 12° forward scatter method.
There are typically a lot of small particles left inside the filtered beer, such as proteins, etc. This colloidal
turbidity will be overvalued with the 90° method, due to the fact that this method is affected more by the
quantity of the particles rather than the particle size. The 12° forward scatter method is affected more by
particle size.
90° method: small particles and large particles will cause comparable scatter light intensities.
12° method: small particles / low scatter light intensity, large particles / high scatter light intensity.
At a particle size of approx. 0.3 µm (formazin) both methods will have approximately equal scatter light
intensities.
The combination of both measurement results informs about the tendency of the particle size distribution.
Measurement value 90°, greater than the measurement value 12°, average particle size smaller as 0.3 µm
Measurement value 90°, less than the measurement value 12°, average particle size larger as 0.3 µm
Particle size
Result 90° scatter light
Result 12° scatter
Larger
0.3 µm
Lower value
Higher value
Smaller
0.3 µm
Higher value
Lower value
Example filtration control:
90° side scatter:
Small particles (e.g. proteins, colloids, etc.) within the filtered beer will be monitored perfectly by the
using the 90° instrument. Using 90° scatter technology, there will be a delay in detecting a filter
breakthrough, since there will be small number of large particles within the filtrate during the initial
stages of filter breakthrough. The total amount of particles will be raised slightly; therefore the
measurement value will be raised slightly as well.
12° forward scatter:
Small particles (e.g. proteins, colloids, etc.) within the filtered beer can be monitored well by the using
the 12° instrument. The beginning of a filter breakthrough will be monitored immediately due to the large
particles (e.g. DE, yeast cells, etc.) within the filtrate. The few large particles will be monitored
immediately and the measurement value will rise sharply. This is also a mass related measurement
principle, which will allow calibration in mg/l if necessary.
