20
CALIBRATION PROCEDURE
The
HI88713
Turbidity bench meter is supplied with 5 AMCO Hanna standards (<0.1 FNU, 15 FNU,
100 FNU, 750 FNU and 2000 NTU) that are specially designed for NTU ratio mode.
The calibration can be done using the supplied calibration solutions for NTU Ratio mode or user
prepared standards for all modes. Turbidity standards have a shelf life and should not be used after
the expiration date. Alternatively, formazin standards can be used. It is recommended that the turbidity
value of the prepared calibration solutions to be close to the default calibration points.
The first calibration point should be near 0 FNU, the second point can be chosen between 10 and 20
FNU, the third point between 50 and 150 FNU, the fourth point between 600 and 900 FNU and the
fifth point between 1500 and 2500 NTU.
FORMAZIN PREPARATION
In order to prepare formazin 4000 NTU stock solution, follow the next procedure:
Solution I : Dissolve 1.000 gram of hydrazine sulfate, (NH2)2 H2SO4, 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, (CH2)6N4, 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.
UNITS CHANGE
(only for
NTU Ratio
and
NTU Non-Ratio
modes)
To change the units for NTU Ratio and Non‑Ratio modes, simply press the “
Unit
” functional key
when a measurement is available. The EBC value is obtained by multiply with 0.245 the NTU value.
