MODEL 2100AN LABORATORY TURBIDIMETER INSTRUMENT ...
MODEL 2100AN LABORATORY TURBIDIMETER INSTRUMENT ...
MODEL 2100AN LABORATORY TURBIDIMETER INSTRUMENT ...
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SECTION 2, continued<br />
2.3.5.2 Addition of Surfactant<br />
Note: Any turbidity contributed by<br />
the addition of surfactant is<br />
negligible.<br />
Limit the use of surfactants (surface-action agents) to severe problems when other<br />
degassing techniques prove ineffective. Surfactants change the surface tension of<br />
the water causing the release of entrained gases. Hach Company recommends a<br />
surfactant such as Triton X-100 (a Rohm and Haas Product, Hach Cat. No.<br />
14096-32) or equivalent. Add one drop of Triton X-100 in the sample cell prior<br />
to sample addition.<br />
This technique is particularly effective when water is supersaturated with air.<br />
Changing the surface tension may accelerate settling of turbidity-causing<br />
particles. Mix the sample well, and measure as soon as possible. Do not mix too<br />
vigorously because the surfactant may begin to foam. Rinse sample cells<br />
thoroughly between measurements to prevent accumulation of residual surfactant<br />
in the cells.<br />
2.3.5.3 Using an Ultrasonic Bath<br />
An ultrasonic bath (Cat. No. 24895-00 or equivalent) is effective in removing gas<br />
bubbles on most samples, especially on viscous liquids . However, the ultrasonic<br />
waves also may alter the characteristics of the turbidity-causing particulates.<br />
Turbidity is dependent on the size, shape, composition, and refractive index of the<br />
suspended particles. Excess application of ultrasound may alter particle size and<br />
shape, and thus change the turbidity. In some instances use of ultrasound may<br />
compound the bubble removal task by fracturing gas bubbles, thus making<br />
degassing more difficult. Use the following ultrasonic bath procedure.<br />
1. Fill a clean sample cell with sample. Leave the cell uncapped.<br />
2. Immerse the cell ( 1/ 2 to 2/ 3 immersed) in an ultrasonic bath, and allow it to<br />
stand until visible bubbles are expelled.<br />
3. Remove the cell and install the cap. Thoroughly dry the cell, and apply a film<br />
of silicone oil.<br />
Note: The time necessary to expel bubbles may vary from a few seconds to a minute or<br />
more. Follow this simple procedure to avoid excessive application of ultrasound. First,<br />
apply ultrasound for a short period of time, and again measure turbidity. Continue for<br />
several repetitions noting the treatment time and turbidity readings. If turbidity begins<br />
to increase instead of decrease, the ultrasound waves probably have started to alter<br />
the suspended particles. Note the treatment time preceding the turbidity increase, and<br />
record it as the maximum time limit for ultrasonic treatment.<br />
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