25
CALIBRATION PROCEDURE FOR RATIO /
NON RATIO TURBIDITY RANGE
HI 83414
has a powerful calibration function that compensates for lamp aging or changing. The
calibration can be done using the supplied calibration solutions or user prepared standards.
HI 83414
turbidimeter is supplied with 5 AMCO standards: <0.1 NTU, 15 NTU, 100, 750 NTU
and 2000 NTU. The Hanna standards are specially designed for this instrument. 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 NTU, the second point can be chosen between 10 and
20 NTU, the third point between 50 and 150 NTU, the fourth point between 600 and 900 NTU 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 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 stand
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 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 discarded 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 turbidity range will
not affect the free or total chlorine measurements.
Before making the calibration, be sure that you are in the correct range.