Data
79
Preparation method of calibration solution
Formazin 4000 NTU
Items to be prepared
Reagent: Sulfuric acid hydrazine CAS 10034-93-2, Molecular formula H
6
N
2
O
4
S (N
2
H
4
H
2
SO
4
)
Reagent: Hexamethylenetetramine, CAS100-97-0 Molecular formula: C
6
H
12
N
4
Balance: One that can measure 100 g with an accuracy of 0.01 g
500 mL beaker
1000 mL measuring flask
Magnetic stirrer
Deionized water: Highly filtered ion-exchanged water
Preparation procedure
1.
Put 5.00 g of sulfuric acid hydrazine in the 500 mL beaker, then add 400 mL of
deionized water and dissolve them.
This will be solution A.
2.
Put 50.00 g of hexamethylenetetramine in the 500 mL beaker, then add 400 mL of
deionized water and dissolve them.
This will be solution B.
3.
Pour solutions A and B into the 1000 mL measuring flask, and add deionized water
until the total quantity reaches 1000 mL.
4.
After stirring the solution using the stirrer for about 15 minutes, stop stirring and
leave the solution at 25
3
C for 24 hours. The solution may be transferred and left
in another glass vessel.
5.
After 24 hours, if the settling of Formazin fills about 80 percent of the vessel, the
solution is prepared.
The turbidity obtained when this solution is stirred is Formazin 4000 degrees (NTU).
The stock solution of Formazin remains stable at 4000 degrees. It can be used at room
temperature for 6 months. However, if it is diluted with deionized water once, the ingredients of
the solution change. As a result, the Formazin clumps together and the value of the turbidity
meter is not stabilized. Therefore, when Formazin is diluted for span calibration, dilute it each
time you perform calibration.
Tip
When Formazin is diluted with the liquid filtered from the supernatant of Formazin of 4000 degrees,
the turbidity of the diluted Formazin can be stabilized.
However, as 4
to 5
of hexamethylenetetramine remains in the Formazin solution, the refractive
index is different in the deionized water and supernatant liquid. Precisely, the value of the turbidity
varies because there are differences in the direction of the transmitted light and amount of scattered
light. Use deionized water to dilute a low-turbidity span solution of Formazin of 5 degrees or lower.
