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FORMAZIN PREPARATION
In order to prepare formazin 4000 NTU stock solution, follow the next procedure:
Solution I : Dissolve 1.000 grams of hydrazine sulfate, (NH
2
)
2
H
2
SO
4
, in distilled, deionized water and
dilute to 100 mL in a volumetric flask.
Warning: Handle hydrazine sulfate with care because it is a carcinogen reagent. Avoid inhalation,
ingestion, or skin contact. Formazin solution can also contain some hydrazine traces.
Solution II : Dissolve 10.000 grams of hexamethylenetetramine, (CH
2
)
6
N
4
, in distilled, deionized water
and dilute to 100 mL in a volumetric flask.
Stock solution: Mix 10 mL Solution I and 10 mL Solution II in a flask. Let the stock solution stays
48 hours at 25 ±3 °C (77 ±5 °F). This will result in a 4000 NTU formazin suspension. It is very
important for the formation of the formazin polymer to maintain the same temperature.
The stock solution (4000 NTU) can be stored up to one year in proper conditions. Store formazin in
amber glass bottle or any UV‑light blocking bottle.
To obtain a high quality formazin always use pure reagents and high‑purity water.
To prepare the calibration standards, dilute the stock solution with the same high‑purity water you
used for the preparation of the stock solution. The diluted formazin solutions are not stable. They
should be used immediately after preparation and discard immediately after use.
CALIBRATION
For best results, the measurement techniques must be followed during calibration. If formazin standards
are used, mix the cuvettes gently for about 1 minute and then allow the standard to settle for 1 more
minute before calibration.
Calibration can be performed in two, three four or five points. Calibration of the ratio turbidity range
will not affect the non ratio turbidity range.
Before making the calibration, assure that you are on the correct range.
To enter calibration, press CAL key while in main
screen. The first screen of GLP information is
displayed. Press the Cal key to start calibration.
It is possible to interupt calibration procedure at
any time by pressing CAL CHECK key.
TWO-POINT CALIBRATION (Ratio and Non Ratio Turbidity)
• The first calibration point is displayed on the LCD as 0.00 NTU.
This point is used to check the quality of the water used for dilution
and to confirm that the optical system is not dirty. If the value of
the first point is over 0.15 NTU, a warning “Cal Point1 high !”
is displayed when the calibration is saved and a warning “Out
of calibration range” is displayed when measurements under
10.0 NTU are performed.
