Serra's fixative does have water in it, the water is from the
formaldehyde. 37% formaldehyde is water saturated with formaldehyde gas
to about 37%.
The precipitate is probably from the buffering compound, phosphate perhaps.
Geoff
Emily Sours wrote:
A related question:
I was making Serra's fix (which has no water in it) and I tried to use
buffered formalin. This turned the solution white (which happens when
Serra's has water in it). Another brand of formalin (which did not
say it was buffered) worked fine.
What's in the buffering that has water in it? Is the methanol diluted
with water in buffered formalin?
The recipe for Serra's is
6ml 100% EtOH
3ml 37% formaldehyde (aka formalin)
1ml glacial acetic acid
Perhaps the buffer in your buffered formalin is causing the
problem--maybe you need unbuffered formalin.
Emily
--
Outside of a dog, a book is man's best friend. Inside of a dog it's
too dark to read.
--Groucho Marx
On Wed, Nov 17, 2010 at 11:42 AM, Geoff McAuliffe <mcaul...@umdnj.edu> wrote:
Commercially purchased 37% formaldehyde has had a small amount (about 1.5% I
think) of methanol added to it for many, many years. It helps to prevent the
polymerization of formaldehyde into insoluble paraformaldehyde. It certainly
does not make the stock solution flammable and it is not contributing to
drying out of your tissues. Those who want methanol-free formalin make it
from paraformaldehyde but for LM there is no point.
Geoff
Jones, Laura wrote:
Greetings to all of you in Histoland. Our lab recently switched from
using a formalin substitute to using 10% Neutral Buffered Formalin. Our
Pathologists have been unhappy with the small tissues, like GI biopsies and
prostate cores. They say they are seeing too much chatter and poor nuclear
detail. We have adjusted our processing times with only mildly better
results.
Today, I arrived at work to find staff cramming boxes and boxes of
prefilled formalin vials into flame cabinets, as JCAHO is here this week.
It occurred to me that 10% NBF was not considered flammable when we used it
years ago, and I was surprised to find that the MSDS for the bottles we had
ordered listed methanol as an ingredient. I immediately went back to my
early days in Histo, when we made up 10% NBF ourselves from 37% concentrate;
and we did not have any alcohol in our "recipe". I thought I had discovered
our whole problem! However, upon further research, we have found that most
prefilled bottles DO contain methanol. The large 20 litre cube, however
does not list methanol as an ingredient.
So, my questions are many. Does that inclusion of methanol contribute to
the drying out of tissues that we are seeing? Does anyone sell prefilled
bottles that contain methanol-free formalin? And, finally, does anyone have
any other thoughts or suggestions? I should add that we use Toluene as our
clearing agent, because our former Pathologist believed it was less harsh on
the tissues; and we are running our tissues on the Thermo Excelsior. We are
running small biopsies and large pieces of tissue together, which I know is
not optimal, but we are a small hospital and one processor is it! I am not
a chemist and would appreciate any advice. Thanks in advance.
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Neuroscience and Cell Biology
Robert Wood Johnson Medical School
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Neuroscience and Cell Biology
Robert Wood Johnson Medical School
675 Hoes Lane, Piscataway, NJ 08854
voice: (732)-235-4583
mcaul...@umdnj.edu
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