7. Push ENTER.
The instrument display
counts down from 60 to
0, and then measures
the standard.
The instrument shows
the next expected
standard (e.g., 20.00).
The mode display
shows "01".
8. Remove the sample
cell from the sample
cell holder.
9. Do steps 5–11 for
the other formazin
standards (from lowest
to highest NTU
standard). Mix each
formazin standard well
and rinse the sample
cell two times with
formazin standard
before the sample cell
is filled.
The mode display
shows "00" after the
last sample cell is
measured.
10. Push CAL/Zero.
The instrument saves
the new calibration data
and goes back to
Measurement mode.
Making 4000-NTU formazin stock solution
W A R N I N G
Chemical exposure hazard. Obey laboratory safety procedures and wear all of
the personal protective equipment appropriate to the chemicals that are handled.
Refer to the current material safety data sheets (MSDS) for safety protocols.
Note: Making formazin stock solution from raw materials is not recommended.
Preparation of formazin stock solution is temperature and technique sensitive. Use
Hach formazin stock solution to get the best instrument performance and analytical
standard accuracy.
1. Dissolve 5.000 grams of reagent grade hydrazine sulfate
((NH
2
)
2
–H
4
H
2
SO
4
) in about 400 mL of demineralized water.
2. Dissolve 50.000 grams of reagent grade hexamethylenetetramine in
about 400 mL of demineralized water.
3. Quantitatively, put the two solutions in a 1-liter volumetric flask, and
dilute to volume with demineralized water. Mix fully.
4. Let the solution stand for 48 hours at 25 ± 1 °C (77 ± 1 °F).
Calibrate the turbidimeter with user-selected formazin
standards
The instrument may be calibrated using user-selected values of formazin
standards.
English 41
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