Measuring Formaldehyde Concentration: The Role of NaOH

[biobird]

Hello all,

In order to re-use formaldehyde from a dilluted solution (in water) I need to know the concentration of formaldehyde in the dilluted solution.
Can anyone tell me how to measure this concentration? It does not have to be very accurate.

thanks in advance,
Albert

 

[lisab]

Hi biobird -

I'm not sure what equipment you have available to you, but here's a wet chemistry method that uses commonly available chemicals. It's from a commonly used test method to measure HCHO from wood products.

You'll need the following solutions:

0.05 M iodine
0.1 M sodium thiosulfate
1.0 M sulfuric acid
starch solution ~1%

Mix 25ml iodine + 10ml NaOH + 20ml of the solution you're testing. Let it sit 15 minutes away from light. Add 15ml H₂SO₄ and titrate immediately with the Na₂S₂O₃. When the solution starts to become pale yellow add a few drops of starch solution as an indicator.

Do the same titration procedure on 20ml water (blank).

Calculate the HCHO concentration:

c[HCHO] = (Vo – V) * 750 * c[Na₂S₂O₃]

Where

Vo = volume of Na₂S₂O₃ used in blank titration, in ml
V = volume of Na₂S₂O₃ used titrating the solution you're testing, in ml
c[Na₂S₂O₃] = concentration of sodium thiosulfate in M (0.1 in this case)
c[HCHO] = concentration of HCHO in mg/L

 

[biobird]

Hello Lisab,

Thank you very much for your description of this procedure.
I will try it soon.
Does the concentration of the NaOH matter?

greetings, Albert

 

[GCT]

Also what kind of instrumentations do you have e.g. Gas Chromatography ?

 

[biobird]

Well, I guess we have this kind of instruments at the lab, but I never worked with it. I was actually looking for a quick and simple method with an accuracy of -let's say- plus/minus 0.5 percent. After all, I'm just a simple biologist

 

[lisab]

Hello Lisab,

Thank you very much for your description of this procedure.
I will try it soon.
Does the concentration of the NaOH matter?

greetings, Albert

Ooops, left that out!

1.0 M NaOH will do.

 

[Kushal]

hi. may i know why NaOH has to be added? - just asking!

thnks