There are three reasons to use paraformaldehyde to make formalin: 

1) Eliminate the methanol preservative of commercial formalin
2) customize the formaldehyde concentration
3) customize the buffer used. 

One of these three variables may affect your test so making your own
allows you to control them. 

If you see a difference in the results when using two "types" of
formalin, consider these variables.



Tim Morken
Technical Support Manager
Lab Vision Products
Anatomical Pathology
Thermo Fisher Scientific


Hello again!

I don't have ANY scientific proof whatsoever of the difference between
10%
formalin and 4% formaldehyde made from PFA. It's just something I think
I
have noticed in the lab, clearly enough to make me wonder. But you are
right
that the fixation protocols were never specifically controlled to allow
real
comparison, so maybe it indeed was some other factor. 

I grew in a developmental biology group and first learnt to use "PFA",
and
eventually started to wonder why some use it and some use formalin
(often
being the same person, for different applications!). Maybe I should
really
investigate it some day. 

With best regards, Mikael

-----------------------------------------------------
 Mikael Niku, PhD, university lecturer            
 University of Helsinki, Division of Nutrition
 URL: mikael.nikunnakki.info

 - What do I think of western civilization?
   I think it would be a good idea!                       
                                            Gandhi
-----------------------------------------------------
-----Original Message-----
From: Tony Henwood [mailto:AnthonyH@chw.edu.au] 
Sent: 22. elokuuta 2008 2:17
To: Mikael Niku; histonet@lists.utsouthwestern.edu
Subject: RE: [Histonet] (para)formaldehyde (was: in situ question)

Why would it be different?
I am intrigued as to why IPX and ISH would reaxct differently in tissues
fixed in either.
Do you have any references?
Or please write up your results and publish them (J Histotechnology or
Biotechnic & Histochem are definitely worth considering).

Often there will be differences but my experience indicates that it is
often
due to the fixation time. 10% buffered formalin is usually used at room
temp, overnight at least, where as researchers for some reason often use
4%
formaldehyde (made from polyformaldehyde) at 4oC for only a few hours at
best. So often fixation occurs in the ethanols in processing.
For valid comparisons fixation conditions must be standardised.

Regards

Tony Henwood JP, MSc, BAppSc, GradDipSysAnalys, CT(ASC) Laboratory
Manager &
Senior Scientist
Tel: 612 9845 3306
Fax: 612 9845 3318
the children's hospital at westmead
Cnr Hawkesbury Road and Hainsworth Street, Westmead Locked Bag 4001,
Westmead NSW 2145 






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