Aqualytic AL400T-WL, Instruction Manual, Page: 22 / 32

22 AL400T-WL_2a 07/2011
2.3.3.2 Measurement of high turbidity values
High turbidity samples with more than 1100 NTU ("overrange") may be diluted. The dilution
water should be a water with very low turbidity.
For accurate dilution proceed as follows:
Mix the water sample well and pipette x ml of the water sample (see table below) into
a 100 ml volumetric flask. Fill with low turbidity water up to mark and mix gently.
Water sample
(x ml)
Multiplication factor
10 10
25 4
50 2
Add the diluted water sample to the vial, perform reading and multiply the displayed result
with the multiplication factor.
Note:
The dilution of the water sample may alter the characteristics of the suspended
particles and produce erroneous results.
2.3.3.3 Measurement of low turbidity values
Accurate and repeatable measurements of low turbidity values depend on exact measurement
techniques.
Use a clean, unscratched and indexed vial. •
Rinse the vial three times with the sample. •
Allow the vial to stand for 1 – 5 minutes so that bubbles can disappear. •
Carefully invert the vial (so that settled particles disperse in the sample). •
Place the vial in the sample chamber and press the [ • ] key (see chapter 2.3.3.5 Indexing
a single sample vial).
Perform multiple measurements, until a reproducible value is displayed (leave the vial in
•
the sample chamber).
Note the smallest steady and reproducible value.
2.3.3.4 Indexing and matching sample vials
The United States Environmental Protection Agency (U.S. EPA) recommends that cuvettes used
for instrument calibration or sample measurement be indexed. To comply with this recom-
mendation, each calibration standard is supplied with an indexing ring and each instrument
has a reference point for quick and repeatable indexing of the calibration standard.
Matched sample vials are required to minimise the effects of optical variation from glass vial to
glass vial. Alternatively an indexed single sample vial can be used for every measurement.