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< 7. Calibration >
7-6
IM 12E01B30-02EN 1st Edition : Mar. 08, 2023-00
c. Make sure that both reagents have been completely dissolved in solutions A and B,
respectively. Pour all of the both solutions (A and B) into a measuring flask (2000 mL) and
mix them together, rinsing the beakers with the deionized water so that no solution is left in
the beakers.
d. Add deionized water up to the marked line of the measuring flask to make the total volume
2000 mL and stir the mixture throughly.
e. Allow the mixed solution to stand for 24 hours at 25 ±3°C.
f. When you find white turbidity or the white precipitation of the mixed solution, stir the mixture
well to use.
The shelf life of 4000 NTU formazine standard solution is one month.
7.3.2 Preparing a 400 NTU Formazin Calibration Standard
Solution
(1) Reagents Required
• Hydrazine sulfate, (NH
2
)
2
·H
2
SO
4
• Hexamethylene tetramine, (CH
2
)
6
·N
4
(2) Equipment Required
• Measuring flask, 2 x 100 mL
• Measuring flask, 1000 mL
• Volumetric pipette, 50 mL
• Analytical balance
(3) Procedure
a. Weigh out 1.000 g ±0.001 g of hydrazine sulfate with a balance, place it in a 100-mL
measuring flask, and add deionized water to make 100 mL (solution A).
b. Weigh out 10.00 g ±0.01 g of hexamethylene tetramine with a balance, place it in another
100-mL measuring flask, and add deionized water to make 100 mL (solution B).
c. Make sure that both reagents have been completely dissolved in solutions A and B,
respectively. Pipette 50 mL each of solutions A and B into a 1000-mL measuring flask and
mix well.
d. Allow the mixed solution to stand for 24 hours at 25 ±3°C.
e. Bring the total volume to 1000 mL with deionized water.
This is a 400 NTU formazin standard stock solution and its storage life is one month. To make a
standard solution of the desired turbidity, dilute this stock solution with deionized water.
7.4 Zero Calibration
Supply Zero water or turn off the light source to perform Zero calibration. See “
n
Zero Standard”
(7.2) to confirm about zero water.
[How to perform Zero calibration]
(1) Turn on the maintenance mode.
(2) Prepare to supply zero water.
<When using zero filter water>
• Open the valve for zero water and let the zero filter water flow.
<For zero calibration by turning off the light source>
This can be selected only when the measured turbidity exceeds 200 NTU.
• Turn off the LED from the maintenance menu.