If you look in the CRC Handbook of Chemistry and Physics under the physical constants of organic compounds they list formaldehyde (or methanal HCHO) as a gas. I agree with you about usage. I ran around about three years ago to the histology department about the "definitions" of formaldehyde, paraformaldehyde and formalin and nobody really knew what the distinction between them was (although most people knew that paraformaldehyde solid was used to make the solution, that you needed to boil the stuff in a chemical fume hood and that after a short period of time it repolymerized and fell out of solution). Histologists just buy the stuff with the methanol in it by the gallon and don't really concern themselves with the chemistry. I use the formalin solution from polysciences for flow and have been very satisified with it. It was recommended by Carleton Stewart in "Flow Cytometry, Second Edition". Margaret >> -----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 >> >> > "The opinions stated above are the authors own, and should not be construed as U.S. Government endorsement of a specific vendor, nor used in any publication to indicate endorsement by the U. S. government or any of its agencies." >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Margaret M. Tropea Critical Care Medicine Department National Institutes of Health (ph) 301-496-7752 (fax) 301-480-3389 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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