Apply Heat; Prevent Condensation On A Sample Cell; Measure Over-Range Samples; Sample Dilution - Hach 2100AN IS User Manual

1. Fill a clean sample cell with sample. Do not put the cap on the
sample cell.
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2. Put / to / of the sample cell into the ultrasonic bath and let it stand
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until visible bubbles are removed.
3. Remove the sample cell from the ultrasonic bath and put the cap on.
4. Fully dry the sample cell.

Apply heat

C A U T I O N
Make sure that the cap on the sample cell is loose. Increasing the temperature of
a tightly-capped sample cell may cause an explosion. More caution should be
taken when increasing the temperature of volatile compounds.
If possible, do not use heat to accelerate degassing. Heat may change
the properties of the suspended particles and cause volatile components
to come out of the solution.
Gentle heat may be used to remove bubbles from very viscous samples
when used with vacuum or ultrasound. If applying heat to the sample is
necessary, do so only as much as is necessary to complete degassing.
Before measurement, decrease the temperature of the sample to the
initial temperature, then gently invert the sample.

Prevent condensation on a sample cell

Condensation may occur on the outside of the sample cell when
measuring a cold sample in a warm, humid environment. This
condensation or fogging of the sample cell interferes with turbidity
measurement.
To prevent condensation:
• Make sure that the outside of the sample cell is dry before
measurement.
• Use the air purge system as necessary. Refer to
system on page 30.
• If condensation occurs while using the air purge system, warm the
sample slightly. Let the sample sit at room temperature or partially put
the sample into a warm water bath for a short time. Gently invert the
sample cell before measurement.
24 English
Note: Warming may change the sample turbidity. Measure the sample without
warming when possible.

Measure over-range samples

The nephelometric method of turbidity measurement depends on light
scattering from suspended particles. If turbidity is very high, significant
amounts of light may be absorbed by the particles, and little light is
available for scattering. This results in a negative interference causing
the measured turbidity to be lower than the actual turbidity. This
condition is called "going blind".
Methods used to prevent the instrument from going blind include:
• Turn Ratio on. Ratio on mode decreases the effects of light absorbing
particles, color, absorbance and high turbidity interferences.
• If measuring in the FNU mode, change the measurement units to NTU
by pushing UNITS/Exit. The NTU measurement mode (with Ratio on)
increases the measurement range.
• Sample dilution. Refer to
When too much light is absorbed by the sample, the lamp icon on the
instrument display flashes.

Sample dilution

Use filtered sample, deionized water or distilled water for sample
dilution. Measure sample dilutions soon after they are prepared.
To prepare filtered sample, use the sample filtration and degassing kit.
Refer to the user instructions provided with the sample filtration and
degassing kit.
If the filters in the sample filtration and degassing kit plug quickly, use a
standard 47 mm filtration apparatus shown in
filter or use a glass-fiber filter. Refer to
After dilution and measurement, calculate the actual turbidity as follows:
Using the air purge
1. Calculate the total volume:
Total volume = sample + dilution water
Example: 20 mL of sample and 80 mL of dilution water
Total volume = 20 mL + 80 mL = 100 mL
2. Calculate the dilution factor:
Sample dilution on page 24.
Figure 6 with a membrane
Accessories on page 47.