[Histonet] formaldehyde concentration

[Peter Noyce]

Thank you
I should give more details -I am not actually doing histology but trying to
find a method to preserve tiny plant shoot apical meristems (approximately
0.05mm cubed in volume) so I can then measure the amount of light organic
elements (CONPS) in a section by using x-ray dispersive spectroscopy with
scanning electron microscopy. I thought a variant of Karnovskys fixative
with no buffer may do it-mix equal amounts of formaldehyde (say 16%% pure
with no methanol and not 10% buffered formalin) and glutaraldehyde (25% EM
grade)-so the formaldehyde penetrates the tiny sample very quickly with fast
initial fixation  and then glutaraldehyde gets in more slowly but gives more
extensive stronger fixation. Am I wrong-will the formaldehyde initially
harden the sample so the glutaraldehyde may not get in ?. Should I use the
lowest formaldehyde concentration that will give initial fixation ( say 8%
which will end up as 4% when diluted with equal amounts of glut.). Please
let me know what you think.
Regards Peter

-----Original Message-----
From: Marcum, Pamela A [mailto:PAMarcum <@t> uams.edu] 
Sent: Wednesday, 31 December 2014 12:51 AM
To: 'Peter Noyce'
Subject: RE: [Histonet] formaldehyde concentration

Peter,

While 20% sounds like it should be faster it is not.  It hardens the outside
of the tissue quickly and can slow penetration to the remainder of the
tissue.  We use 4% which if you start full strength liquid formaldehyde
actually with 1 part formaldehyde and 9 parts buffer or water is 3.7% that
we can 10% formalin.  It is a real issue as we are basing the 10% number on
the amount of formaldehyde (37 - 40%) added to buffer or water not the
actual amounts.  Sorry it is confusing about amounts.  Let me know if you
need more information or this sounds dodgy.

Pam

-----Original Message-----
From: histonet-bounces <@t> lists.utsouthwestern.edu
[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Peter Noyce
Sent: Monday, December 29, 2014 6:27 PM
To: histonet <@t> lists.utsouthwestern.edu
Subject: [Histonet] formaldehyde concentration

I am using pure formaldehyde with no methanol and unbuffered as a first
fixative. It comes in concentrations from 20% to 4%. From my reading; 1)it
seems the higher strength penetrates faster ?. 2)4% is the minimum strength
to get good penetration ?.

Peter Noyce PhD student Australia.

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