22
CALIBRATION PROCEDURE
HI 98703
has a powerful calibration function that compensates for lamp aging or changing. The
calibration can be done using the suplied calibration solutions or user prepared standards.
HI 98703
turbidimeter is supplied with 4 AMCO standards: <0.1 NTU, 15 NTU, 100 NTU and 750
NTU. 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 NTU. The second point can be chosen between 10 and 20 NTU, the
third point between 50 and 150 NTU and the fourth point between 600 and 900 NTU.
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.
If the prepared formazin is used, enter the actual standard value by pressing
s
or
t
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 cuvettes 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
.
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