RE: [Histonet] (para)formaldehyde

From:"Tony Henwood"

I agree


Tony Henwood JP, MSc, BAppSc, GradDipSysAnalys, CT(ASC)
Laboratory Manager & Senior Scientist
Tel: 612 9845 3306
Fax: 612 9845 3318
the children's hospital at westmead 
Cnr Hawkesbury Road and Hainsworth Street, Westmead 
Locked Bag 4001, Westmead NSW 2145 

-----Original Message-----
[] On Behalf Of MKing
Sent: Saturday, 30 August 2008 12:15 AM
Subject: [Histonet] (para)formaldehyde

The statement that 4% paraformaldehyde solution contains nothing but 
water and formaldehyde is simply not true: as has been discussed 
thoroughly and often on Histonet (see archives), formaldehyde in aqueous

solution spontaneously decomposes.  This is precisely why formalin 
solutions are used, with methanol 'parking' the chemical reaction. 
Without measurement one never knows exactly how much formaldehyde is 
really present in solutions made from paraformaldehyde, although freshly

made solutions will have concentrations closest to 4%.  It is highly 
improbable that 3.8 and 4.0% solutions would produce any detectable and 
reproducible differences on any histological procedure, although the 
methanol added to formalin might.

Mike King
UF Pharmacology & Therapeutics

Message: 5
Date: Wed, 27 Aug 2008 17:26:19 -0400
From: "Monfils, Paul" 
Subject: RE: [Histonet] (para)formaldehyde
Content-Type: text/plain;	charset="iso-8859-1"
10% formalin and 4% paraformaldehyde are interchangeable for most 
purposes (in histology at least).  However there are a couple of minor 
differences.  First, commercial formaldehyde solution contains 37% to 
38% formaldehyde.  Therefore diluting it 1:9 results in a solution 
containing 3.7% to 3.8% formaldehyde, while a 4% solution of 
paraformaldehyde in water contains a full 4% formaldehyde.  Secondly, 
commercial formaldehyde solution contains 10% to 15% methanol as a 
preservative.  Therefore diluting it 1:9 results in a solution 
containing 1.0% to 1.5% methanol.  This is not a problem for most 
histological applications, but it could be a problem in a procedure 
where sources of methylation have to be avoided.  4% paraformaldehyde 
solution contains no methanol - nothing but water and formaldehyde.

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