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Instructions for the Preparation of Standard Solutions
Standard solution of formaldehyde
Preparation of a stock solution:
In a calibrated or conformity-checked 1000-ml
volumetric flask make up 2.50 ml of formaldehyde
solution min. 37 % GR to the mark with distilled
water. The stock solution prepared according to
this procedure has a concentration of approxi-
mately 1000 mg/l formaldehyde.
Precise assay of the standard solution (stock
solution) for formaldehyde:
Pipette 40.0 ml (full pipette) of the formaldehyde
stock solution of approximately 1000 mg/l into a
300-ml ground-glass conical flask, and add
50.0 ml (buret) of iodine solution 0.05 mol/l and
20 ml of sodium hydroxide solution 1 mol/l.
Leave to stand for 15 minutes and subsequently
add 8 ml of sulfuric acid 25 % GR. Add 1 ml of zinc
iodide-starch solution and subsequently titrate to
the end point with sodium thiosulfate solution
0.1 mol/l.
Calculation of the exact content of the
formaldehyde solution:
C1 = consumption of sodium thiosulfate solution
0.1 mol/l
C2 = quantity of iodine solution 0.05 mol/l
mg/l Formaldehyde = (C2 – C1)
Further investigational concentrations may be pre-
pared from the stock solution exactly determined
according to the procedure described above by
diluting accordingly.
Stability:
When stored in a cool place (refrigerator), the
stock solution remains stable for one week. After
this time, the stock solution must be determined
anew and the corresponding value must be duly
accounted for in the further use. The diluted in-
vestigational solutions must be used immediately.
Reagents required:
1.04003.1000 Formaldehyde solution min.
37 % GR for analysis
1.09099.1000 Iodine solution 0.05 mol
I2/l 0.1 N solution
1.09147.1000 Sodium thiosulfate solution
0.1 mol/l 0.1 N solution
1.09137.1000 Sodium hydroxide solution
1 mol/l 1 N solution
1.00716.1000 Sulfuric acid 25 % GR for analysis
1.05445.0500 Zinc iodide-starch solution GR
for analysis
1.16754.9010 Water GR for analysis
Release 05/04
37.525
x
Standard solution of hydrazine
Preparation of a standard solution:
Dissolve 4.07 g of hydrazinium sulfate GR with
oxygen-low (boil previously) distilled water in a
calibrated or conformity-checked 1000-ml
volumetric flask and make up to the mark with
distilled water. The stock solution prepared
according to this procedure has a concentration
of 1000 mg/l hydrazine.
Further investigational concentrations may be
prepared from this stock solution by diluting
accordingly.
Stability:
When stored in a cool place (refrigerator), the
stock solution and the further diluted investiga-
tional solutions remain stable for one day.
Reagents required:
1.04603.0100 Hydrazinium sulfate GR
for analysis
1.16754.9010 Water GR for analysis
XXIII
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