FriendlyFinger
Hazard to Self
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Registered: 14-3-2005
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Sodium sulfite method for formaldehyde
Can anybody please show me where I can find details on how to determine formadehyde concentration in formalin?
I have searched google and there are lots of reference to F. Walker and the sodium sulfite method, but I don't see any expanation.
Thanks.
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Ozone
International Hazard
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Look up EPA 8315 (via 2,4-dinitrophenylhydrazine in acetate buffer at pH 5) or, more conveniently, chromotropic acid in H2SO4 (conc.) which provides a
relatively handy colorimetric test (purple).
What you are thinking of would be via formation of the water soluble organosulfite via sodium bisulfite. I have never used this as a quantitative
method, but I have useed it to purify aldehydes and methyl ketones. Here, the sulfite is made and extracted from the mix with water. The water is then
treated with acid or base (and heat) to yield the purified aldehyde or ketone (hopefully) as an easily separable organic layer. grams, not micrograms.
I suppose you could hit the sample with bisulfite (a known amount) and back titrate the residual SO2 using rosaniline, but I suspect this to be
tedious and error-prone. Perhaps a redox titration with peroxide/KI using a starch indicator?
Go with the chromotropic acid method.
Cheers,
O3
[Edited on 18-12-2007 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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chloric1
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Speaking of formaldehyde, is it possible to detect this compound in the presense of natural and artificial sweeteners?Many sugars have active aldehyde
groups.
I was pondering one day about decomposing aspartame in diet cola by boiling to see if formaldehyde could be detected.
Fellow molecular manipulator
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Klute
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Registered: 18-10-2006
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To titrate dilute formaldehyde solutions (just dilute your stock, and calculate initial concentration afterwards), we use a know amount of basic I2/I-
(dismutes to IO3- and I-), leave to react with the formaldehdye solution in the dark for 10-15min, acidify (IO3- back to I2), and back-titrate the
formed I2 with thiosulfate.
From the amount of I2 consumed, calculate the concentration of your formaldehdye solution. Leaev the flasks in the dark and the cold, and consider
the that reaction stops at the formic acid stage (IIRC).
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Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
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To titrate dilute formaldehyde solutions (just dilute your stock, and calculate initial concentration afterwards), we use a know amount of basic I2/I-
(dismutes to IO3- and I-), leave to react with the formaldehdye solution in the dark for 10-15min, acidify (IO3- back to I2), and back-titrate the
formed I2 with thiosulfate.
From the amount of I2 consumed, calculate the concentration of your formaldehdye solution. Leaev the flasks in the dark and the cold, and consider
the that reaction stops at the formic acid stage (IIRC).
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