439
Interferences
Summary of Method
This turbidity test measures an optical property of the sample
which results from scattering and absorption of light by particles
in the sample. The amount of turbidity measured depends on
variables such as the size, shape, color, and refractive properties
of the particles.
This procedure is calibrated using formazin turbidity standards
and the readings are in terms of Formazin Attenuation Units
(FAU). This test cannot be used for USEPA reporting purposes,
but it may be used for daily in-plant monitoring. One FAU is
equivalent to one Nephelometric Turbidity Unit (NTU) of
Formazin. However, the optical method of measurement for FAU
is very different than the NTU method (1 NTU =
1 FTU = 1 FAU when traced to formazin primary standards.)
REQUIRED APPARATUS
Quantity Required
Description Per Test Unit Cat. No.
Sample Cell, 10-20-25 mL, w/cap ................................2 .........................6/pkg..........24019-06
REQUIRED REAGENTS
Description Units Cat. No.
Formazin Stock Solution, 4000 NTU.................................................... 500 mL............2461-49
Silicone Oil........................................................................................15 mL DB............1269-36
StablCal Stabilized Turbidity Standard, 200 NTU................................ 500 mL..........26604-49
Water, deionized........................................................................................... 4 L..............272-56
Interfering Substance Interference Levels and Treatments
Air Bubbles Interfere at all levels. Degass samples using the
Degassing Kit or an ultrasonic bath.
Color Interferes if the color absorbs light at 520 nm.
Temperature extremes May interfere by changing the turbidity of the sample.
Analyze samples as soon as possible after collection.
Analyze at the same temperature as the original sample.
TURBIDITY, continued
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