> -----Original Message----- > From: DARZYNKIEWICZ ZBIGNIEW [SMTP:DARZYNK@nymc.edu] > Sent: Wednesday, May 31, 2000 4:34 PM > To: Cytometry Mailing List > Subject: FW: paraformaldehyde vs formaldehyde > > > > > > A year ago I responded to similar querry about paraformaldehyde vs > > formaldehyde. I am enclosing my response below.. > > > > > > -----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 Brander Cancer Research Institute New York Medical College 19 Bradhurst Ave. Hawthorne, NY 10532 tel: 914-347-2801 fax: 914-347-2804 http://www.geocities.com/z_darzynkiewicz > > >
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