Analytical Method: Analytical Quality Assurance, Standard for Formaldehyde

Reagents:
Cat.No. 104003  Formaldehyde solution min. 37 % for analysis
Cat.No. 109099  Iodine solution 0.05 mol I2/l 0.1 N solution
Cat.No. 109147  Sodium thiosulfate solution 0.1 mol/l 0.1 N solution
Cat.No. 109137  Sodium hydroxide solution 1 mol/l 1 N solution
Cat.No. 100716  Sulfuric acid 25 % for analysis
Cat.No. 105445  Zinc iodide-starch solution for analysis
Cat.No. 116754  Water for analysis
 
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 % to the mark with distilled water. The stock solution prepared according to this procedure has a concentration of approximately 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 %. 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) x 37.525

Further investigational concentrations may be prepared 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 investigational solutions must be used immediately.
 

For use with test kits:

 

Measuring range
in mg/l

110036

MQuantTM Formaldehyde Test

10 - 100

108028

MColortestTM Formaldehyde Test

0.1 - 1.5

116989

Reflectoquant® Formaldehyde Test

1.0 - 45.0

114500

Spectroquant® Formaldehyde Cell Test

0.10 - 8.00

114678

Spectroquant® Formaldehyde Test

0.02 - 8.00

 

 


 

Materials

     
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