hello William, yes there certainly is a difference between formaldehyde &
paraformaldehyde that may alter your immunohistochem. data.
1) formulin (3.7% formaldehyde) : this sounds like a 1 in 10 dilution of
the stock formulin soln from histology labs.is it a buffered soln, if so,
is the buffer right for you? formulin usually has substantial contamination
with methanol (I'm not sure why although I'd guess that it's a left over
from the formaldehyde synthesis.) some antigens are metOH sensitive, others
are not, it depends on your system.Also, this stuff can be held in liquid
form for years , so it may not be all f-aldehyde any more.
2)formaldehyde & p- formaldehyde are not the same, as I think that p-form
is more stable & is a polymeric form of formaldehyde. when you make a 4%
soln of p-form ,you are depolymerizing it to give the formaldehyde, which
then loses its reactivity rapidly (hours), so that's why the recipe books
specify fresh solns of p-form.
3) on the bright side, all of these reagents are dead easy to purchase, the
histo lab catalogues would be a good place to look for suppliers.