> A year ago I responded to similar querry about paraformaldehyde vs > formaldehyde. I am enclosing my response below.. > PS. The "fixation efficiency" in terms of the rate of crsosslinking and other formaldehyde reactions should be quite similar in solutions that contain methanol-free formaldehyde vs. formaldehyde with minor contamination of methanol (e.g. about 0 3% methanol at 1 % formaldehyde concentration) > > -----Original Message----- > From: DARZYNKIEWICZ ZBIGNIEW [SMTP:DARZYNK@nymc.edu] > Sent: Friday, May 21, 1999 2:52 PM > To: Cytometry Mailing List > Subject: paraformaldehyde vs formaldehyde > > > Paraformaldehyde is a polymerized form formaldehyde. It is hardly soluble > and it cannot be used as a fixative. Only formaldehyde is used as a > fixative. However, formaldehyde in aqueous solutions spontaneously > polymerizes. Therefore, methanol is often added to slowdown the > polymerization reaction. Solutions of formaldehyde (usually ~ 37%) in > water, > containig 10-15 % methanol as a preservative are generally called > "formaldehyde"; such solutions are being sold by most reagent companies. > Solutions further diluted (4-10 %) received name "formalin". > Methanol-free formaldehyde, which sometimes is preferred (e.g. for fixing > cells for some some histochemical reactions or in immunocytochemistry), > can > be obtained by hydrolysis of paraformaldehyde. This is usually done by > extensive heating of paraformaldehyde solutions. Because of this procedure > the methanol-free formaldehyde received (incorrrectly) the name > "paraformaldehyde". In the past, this was the most common way to obtain > methanol-free formaldehyde. Unfortunately, this incorrect name is still > often used in the literature, generating the confusion. The methanol-free > formaldehyde solutions can now be purchased. Some are called "ultrapure". > We > purchase such solutions (10%) from Polysciences, Inc. (800-523-2575); they > can be stored at room temperature. I would not recommend, however, to > store > them longer than one year, since formaldehyde in these solutions still has > tendency to polymerize. It should be noted that all formaldehyde solutions > are highly toxic and carcinogenic. > Zbigniew Darzynkiewicz > >
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