Hanna Instruments HI 98713 User Manual

Page 12

TWO-POINT CALIBRATION
• Turn the instrument on by pressing ON/OFF.

When the LCD displays dashes, the instrument
is ready.

• Enter calibration mode by pressing CAL.

The display will show “CAL P.1” and no
suggested value. This first point is used to
check the optical system.

• Place the <0.1 FNU standard cuvet into the

holder and ensure that the cuvet mark is aligned
with the sign on the instrument top.

• Close the lid and press READ . The display

will show blinking dashes and the icons for
cuvet, detectors and LED will appear during
measurement. Alternatively, press LOG/CFM to
skip the first point.

• The second calibration point (15.0 FNU) is

then displayed on the primary LCD, “CAL P.2”
on the secondary LCD, and “READ” tag will
blink.

• If the prepared formazin is used, edit the

displayed value by pressing UP or DOWN keys
until the display shows the correct value.

• Remove the first standard cuvet and place the

15.0 FNU standard cuvet (or the prepared one)
into the holder and ensure that the cuvet mark
is aligned with the sign on the instrument top.

• Close the lid and press READ . The display

will show blinking dashes and the icons for
cuvet, detectors and LED will appear during
measurement.

CALIBRATION PROCEDURE

HI 98713 has a powerful calibration function that compensates for LED aging or changing. The
calibration can be done using the suplied calibration solutions or user prepared standards.
HI 98713 turbidimeter is supplied with 4 AMCO standards: <0.1 FNU, 15 FNU, 100 FNU and
750 FNU. The Hanna standards are specially designed for this instrument. The 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 prepared calibration
solutions to be close to the default calibration points.
The first 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 and the fourth point between 600 and 900 FNU.

FORMAZIN PREPARATION
In order to prepare formazin 4000 FNU stock solution, follow the next procedure:

Solution I

Dissolve 1.000 grams 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 FNU formazin suspension. It
is very important for the formation of the formazin polymer to maintain the same temperature.

The stock solution (4000 FNU) 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.
If the prepared formazin is used, enter the actual standard value by pressing UP or DOWN key to edit
the value of the second, third or fourth calibration point.

CALIBRATION
For best results, the measurement techniques must be followed during calibration. If formazin
standards are used, mix the cuvets gently for about 1 minute and then allow the standard to settle for
one more minute before calibration.
Calibration can be performed in two, three or four points. It is possible to interupt calibration
procedure at any time by pressing CAL or ON/OFF.