RE: [Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde(lengthy)

From:"Weems, Joyce"

And all this time I thought it was how to dress for a party. I could have blown up! Have a good weekend everyone... j:>)-----Original Message-----From:[]On Behalf Of BryanHewlettSent: Friday, February 04, 2005 2:55 PMTo: Morken, Tim - Labvision; histonet@lists.utsouthwestern.eduSubject: Re: [Histonet] RE: Formaldehyde vs Formalin vsparaformaldehyde(lengthy)Tim,"Formal" is quite different, it is another name for Methylal(dimethoxymethane) a flammable colourless, volatile liquid used as asolvent.Bryan----- Original Message -----From: "Morken, Tim - Labvision" To: Sent: Friday, February 04, 2005 2:33 PMSubject: RE: [Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde(lengthy)> I think "Formalin" and "Formal" were trade names from a company and just> went into common usage.>>> Tim Morken>> -----Original Message-----> From:> [] On Behalf Of Bryan> Hewlett> Sent: Friday, February 04, 2005 11:24 AM> To:> Subject: [Histonet] RE: Formaldehyde vs Formalin vs paraformaldehyde> (lengthy)>>> I was hoping that John Kiernan would jump in reply to this issue with his> usual eloquence! However, here goes.>> Confusion in terminology has been common since Blum introduced this agentas> a fixative in 1893! It never ceases to amaze me that this should be so,the> issue has been repeatedly addressed in all major Histotechnology textssince> before the early fifties ( my student days in the UK).>> The following information is from the 10th Edition(1981) of the Condensed> Chemical Dictionary and the10th Edition(1983) of the Merck Index (the only> ones at hand).>> Formaldehyde is a gas.> It is readily soluble in water up to 55% and is commercially available tous> as 37%, 44% and 50% aqueous solutions which may contain up to 15%methanol.> These commercial grades are called Formalin.>> Formaldehyde solution (Merck Index)> The USP grade is about 37% (37-40%)  w/v formaldehyde gas in water,usually> with 10-15% methanol added to prevent polymerization. This solution is> considered to be full strength and is also known as Formalin 100% or> Formalin 40 which signifies that it contains 40 grams of formaldehydewithin> 100mL of the solution. It is this solution that produces most of the> confusion since it is referred to and thought of as 100% Formalin.>> Paraformaldehyde (Merck Index)> A white crystalline powder of polymerized formaldehyde, obtained by> concentrating formaldehyde solution. Upon solution in waterdepolymerization> and evolution of formaldehyde occurs. Thus an aqueous solution containing4> grams of paraformaldehyde is essentially the same as a solution of 4%> formaldehyde. There is NO such thing as a solution of paraformaldehyde.> Right John?>> The concentration of formaldehyde used for fixation has been the subjectof> much confusion (see above). The concentration of formaldehyde in compound> fixatives varies widely - ranging from 0.5 to 15% w/v. The majority of> fixatives, using formaldehyde as the sole fixative agent, have a> concentration of formaldehyde between 2.5 and 4% w/v. The concentration of> formaldehyde in a fixative should be stated as the percentage by weight of> the gas, rather than as a percentage of the> formalin(sic) or paraformaldehyde(sic) used to prepare it.>> Thus:> "4% formaldehyde" - not 10% formalin.> "4% formaldehyde, from paraformaldehyde" -  not 4% paraformaldehyde. "NBF> means Neutral buffered formaldehyde" - (not formalin) and is 4% w/v> formaldehyde in phosphate buffer pH 7.0- 7.2.>> Bryan Hewlett>> Consultant Technologist> QMP-LS>>>>>>> _______________________________________________> Histonet mailing list>>>> _______________________________________________> Histonet mailing list>>>_______________________________________________Histonet mailing listHistonet@lists.utsouthwestern.edu Notice ** The information contained in this message may be privileged and is confidential information intended for the use of the addressee listed above. If you are neither the intended recipient nor the employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any disclosure, copying, distribution or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this communication in error, please notify us immediately by replying to the message and deleting it from your computer.Thank you. Saint Josephs Health System, Inc.

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