[Histonet] quick question about formaldehyde

[LuAnn Anderson]

At 12:43 PM 5/13/05, LuAnn Anderson wrote:
>Hi Joyce,
>That is exactly what we were taught. formaldhyde=37% and formalin=10%
>LuAnn
>
>
>
>>For all my years I have believed that formaldehyde was the 37% 
>>concentrate without buffers, and that formalin was 10% buffered... learn 
>>something new every day! Thanks John! -----Original Message----- From: 
>>John A. Kiernan [mailto:jkiernan <@t> uwo.ca] Sent: Friday, May 13, 2005 11:31 
>>AM To: Weems, Joyce Cc: histonet <@t> lists.utsouthwestern.edu Subject: Re: 
>>[Histonet] quick question about formaldehyde Dear Joyce, Formalin = 37% 
>>formaldehyde; so no, it doesn't make a difference. Formalin is not 
>>buffered; it does contain about 10% methanol, which is put in to retard 
>>polymerization. When diluted to make a 4% formaldehyde fixative, the 
>>methanol concentration is 1%. Buffering of the dilute solution offsets pH 
>>changes due to the Cannizzaro reaction. It also inhibits the formation of 
>>blood-derived "formalin pigment" which forms after fixation in an acidic 
>>formaldehyde solution. Tim Morken is correct in saying we don't know the 
>>extent of chemical change in 12 year-old formalin. The fact that there's 
>>no expiry date sugggests that it's not much. For what it's worth, I've 
>>used formalin that's more than 5 years old and fixation has been 
>>OK.                       John Kiernan                       london, 
>>Canada ---------------------------------------------- "Weems, Joyce" 
>>wrote: > > Also, John said "formalin" - was the solution formalin or 37% 
>>formaldehyde  - without buffers? Would that make a difference? > > 
>>Joyce > > -----Original Message----- > From: 
>>histonet-bounces <@t> lists.utsouthwestern.edu > 
>>[mailto:histonet-bounces <@t> lists.utsouthwestern.edu]On Behalf Of Morken, > 
>>Tim - Labvision > Sent: Thursday, May 12, 2005 2:08 PM > To: 'John 
>>Kiernan'; Andrea Grantham > Cc: histonet <@t> lists.utsouthwestern.edu > 
>>Subject: RE: [Histonet] quick question about formaldehyde > > John,  you 
>>said "   Small amounts of methanol and formate ions are not going > to 
>>change the fixative properties." > > But after 12 years  will it really 
>>be a "small amount?" How do we know what > percentage of the solution 
>>will have been converted? > > Tim Morken > > -----Original Message----- > 
>>From: histonet-bounces <@t> lists.utsouthwestern.edu > 
>>[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of John 
>>Kiernan > Sent: Thursday, May 12, 2005 10:48 AM > To: Andrea Grantham > 
>>Cc: histonet <@t> lists.utsouthwestern.edu > Subject: Re: [Histonet] quick 
>>question about formaldehyde > > Two things could have happened to 
>>unopened > formalin in 12 years: > 1. Polymerization (to 
>>paraformaldehyde). This is >    evident as a white precipitate. It 
>>slightly >    reduces the concentration in the liquid, >    but that does 
>>not matter for fixation. >    Polymerization is accelerated by low 
>>room >    temperature, and it is claimed that the >    process can be 
>>reversed by autoclaving(paper >    in Stain Technol about 40 years 
>>ago). > 2. Cannizzaro's reaction, in which 2 molecules >    of 
>>formaldehyde react together, producing >    one molecule each of methanol 
>>and formic >    acid. This happens in all formaldehyde solutions >    and 
>>causes lowering of the pH. This doesn't matter >    if you make a neutral 
>>buffered fixative solution. >    Small amounts of methanol and formate 
>>ions are not >    going to change the fixative properties. > Bottom line: 
>>OK to use, but be sure to check the > pH of the working fixative solution 
>>and adjust if > necessary. > -- > ------------------------------- > John 
>>A. Kiernan > Department of Anatomy and Cell Biology > The University of 
>>Western Ontario > London,   Canada   N6A 
>>5C1 >    kiernan[AT]uwo.ca >    http://publish.uwo.ca/~jkiernan/ > 
>>http://instruct.uwo.ca/anatomy/530/index.htm > 
>>_______________________________ > Andrea Grantham wrote: > > > > One of 
>>the labs here is closing and they have a case of formaldehyde, > > 37.5%, 
>>that they are trying to give away. They have had it in their > > lab 
>>since 1993. The bottles have not been opened. Is it still good to > > 
>>use? Andi > > 
>>..................................................................... > > 
>>: Andrea Grantham, HT(ASCP)     Dept. of Cell Biology & Anatomy     : > > 
>>: Sr. Research Specialist       University of Arizona               : > > 
>>: (office:  AHSC 4212)          P.O. Box 245044                     : > > 
>>: (voice:  520-626-4415)        Tucson, AZ  85724-5044    USA       : > > 
>>: 
>>(FAX:  520-626-2097)          (email:  algranth <@t> u.arizona.edu) 
>>: > > 
>>:...................................................................: > > 
>>            http://www.cba.arizona.edu/histology-lab.html > > > > 
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>>5C1    kiernan[AT]uwo.ca    http://publish.uwo.ca/~jkiernan/ 
>>http://instruct.uwo.ca/anatomy/530/index.htm 
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