Hanna Instruments HI 88713 User Manual

Page 11

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 up to five points, independently, for each mode. The calibration
points are:

FNU mode:

0, 15, 100, 750

FNU

FAU mode:

15, 100, 750, 2000 FAU

NTU ratiometric mode:

0, 15, 100, 750, 2000 NTU

NTU non-ratiometric mode: 0, 15, 100, 750

NTU

Before making the calibration, assure that you are in the correct mode.
To enter calibration, press CAL key while in main screen. The first screen of GLP
information is displayed. Press “Cal” functional key to start calibration.
It is possible to interupt calibration procedure at any time by pressing CAL or ESC key.

FIRST POINT CALIBRATION
•

The first calibration point is displayed on the LCD.

This point is used for FNU and NTU modes to check the quality of the water used for dilution and to
confirm that the optical system is not dirty. In this case, if the value of the first point is over 0.15 FNU
(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 FNU (NTU) are performed.

CALIBRATION PROCEDURE

The HI 88713 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, (NH

)

, 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)

, 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.