Talk:Fixation (histology)

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Wiki Education Foundation-supported course assignment

This article was the subject of a Wiki Education Foundation-supported course assignment, between 31 August 2021 and 16 December 2021. Further details are available on the course page. Student editor(s): J dotter. Peer reviewers: Dinoboy10, JdanR.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 21:29, 16 January 2022 (UTC)[reply]

Fixation and artifacts

All chemical fixation techniques for histology introduce artifacts. Medical facilities often strictly control processing techniques (or they're set by governing bodies) to account for this. Good references can probably be found. A more recent reference on mesosomes was added. --69.226.108.255 (talk) 03:04, 8 March 2008 (UTC)[reply]

There is an inaccurate statement in the article. Neutral buffered formalin is not made using phosphate buffered saline. Neutral buffered formalin is made using phosphate buffers, but no chlorides are involved. Sodium phosphate, monobasic, monohydrate and sodium phosphate, dibasic, anhydrous are the compounds used. This can be checked in "Theory and Practice of Histological Techniques", edited by John Bancroft and Marilyn Gamble. The author of the existing passage has clearly confused NBF with saline buffered formalin. — Preceding unsigned comment added by 77.254.69.155 (talk) 14:09, 31 January 2013 (UTC)[reply]

Paraformaldehyde is only a stable form with long shelf life for storage, it is not a fixative at all. In order to use it, you have to de-polymerize it first by heat and/or basic conditions (NaOH), to get a solution of formaldehyde in water, which is the active fixative. Two reasons why you would go to that trouble: formaldehyde solutions are not stable, but tend to polymerize back to oligo- and paraformaldehyde. To prevent this, the infamous substance sold as "formalin" contains up to 15% methanol, and often also carbonates (marble flakes etc.) to buffer against the formic acid, that gradually builds up by auto - oxidation of formalin under light. All three adittional compounds might interfere with your reaction, so if you need precise results (e.g. in EM work), you de-polymerize the paraformaldehyde directly before use. In addition, "Formalin" is max. 37-40% formaldehyde (no one knows exactly how much) in water, so, a bulky, heavy, unstable liquid. Paraformaldehyde, on the other hand, is a pure, light, stable powder with unlimited shelf life. So there you go.... Addendum: dissolved formaldehyde actually reacts rapidly with water to form methanediol (methylene glycol). It is an equilibrium reaction that leaves very little free formaldehyde in the solution. Consequently, "4% formaldehyde in water" is actually ~3.9% methanediol and 0.1% formaldehyde. That is one of the reasons, why formaldehyde penetrates fast, but needs a long time to actually properly fix tissue, because only the 0.1% available formaldehyde react with tissue, then the reaction hast to "wait" for the equilibrium to shift back to provide "new" formaldehyde for the formaldehyde-protein reaction.
<ref>https://precym.mio.univ-amu.fr/spip.php?article160</ref></ref>
<ref>https://journals.sagepub.com/doi/pdf/10.1177/33.8.3894502</ref>
134.34.122.37 (talk) 14:25, 1 July 2019 (UTC)[reply]

Merger proposal

I came across the article Heat fixation, and I think its info should be moved here. It would fit nicely under the Types of fixation section, in my opinion. raven1977 (talk) 14:52, 5 October 2008 (UTC)[reply]

I have added a small amount of information from the other article to the Type of Fixation section. If anyone objects, or if I'm wrong and the subject does not belong there, feel free to remove/move it. raven1977 (talk) 15:01, 5 October 2008 (UTC)[reply]

References

There are no references provided for the "Factors Affecting Fixation" section (i.e. appropriate pH, responsibility of underfixation for inappropriate results in some assays). There are actually very few references for the article in general, so it would be helpful to add more sources. Rawkergirl (talk) 19:14, 4 November 2010 (UTC)[reply]
<ref>https://www.sciencedirect.com/science/article/pii/S0022532074800249</ref>
<ref>https://www.sciencedirect.com/science/article/pii/S0022532075800141</ref>
<ref>http://www.sciencedirect.com/science/article/pii/S0022532066801090</ref>
134.34.122.37 (talk) 15:01, 1 July 2019 (UTC)[reply]

Karnovsky fixative

For article Karnovsky fixative, I added into a "See also" section. If any expert who is more knowledgeable of this topic would like to move to another spot in Fixation article, please do so. This subject is 100-percent out of my wheelhouse. Thanks. JoeNMLC (talk) 00:31, 16 December 2021 (UTC)[reply]