Reference data
65
Preparation method Formazin 4000 FTU
Q
Setup and preparation
Items to be prepared
z
Agent: Sulfuric acid hydrazine, CAS 10034-93-2, Molecular formula: H6N2O4S
(N2H4•H2SO4)
z
Agent: Hexa methylene tetramine, CAS 100-97-0, Molecular formula: C6H12N4
z
Balance: The one that can measure 100 g with accuracy of 0.01 g.
z
500 mL beaker
z
1000 mL female flask
z
Magnetic stirrer
z
Purified water: The one highly filtered by iron-exchanged water
1.
A liquid: Put 5.00 g of sulfuric acid hydrazine in the 500 mL beaker, add about 400
mL of deionized water, and dissolve them.
2.
B liquid: Put 50.00 g of Hexa methylene tetramine in the 500 mL beaker, add 400 mL
of deionized water, and dissolve them.
3.
Pour A liquid and B liquid into the 1000 mL female flask, add deionized water until
the total quantity reaches 1000 mL.
4.
Stir the solution with the stirrer for about 15 min, stop the stirring, and leave the
solution at 25
°
C ±3
°
C for 24 h.The solution may be transferred and left in another
glass vessel.
5.
After 24 h, if the settling of Formazin fills about 80 percent of the vessel, the
solution is prepared.
The turbidity obtained when this solution was stirred is Formazin 4000 degrees (FTU).
The stock solution of Formazin remains stable at 4000 degrees. The stock solution can be
used at a room temperature for six months. When it is diluted with deionized water once, the
components of the internal solution change, so the Formazin clumps together. The value of
the turbidity meter does not stay constant. Therefore, when Formazin is diluted for span
calibration, dilute it each time you perform calibration.
Reference
When Formazin is diluted with the liquid filtered from the top solution of Formazin of 4000 degrees,
the turbidity of the diluted Formazin can be stabilized. However, 4% to 5% of Hexa methylene
tetramine remains in Formazin liquid, so the refractive index is different in the purified water and the
top liquid. Precisely, the value of turbidity is different because it is affected by the advance of
transmitted light and an scattering amount of light. Dilute a low-turbidity span solution of Formazin of
five degrees or lower with purified water.
