[Histonet] Formalin pH

[John Kiernan]

You can check the pH with a pH meter. This is the most accurate way, but the meter's electrode must be calibrated against at least two standard (usually bought) buffer solutions, such as 4.0 and 7.0.  If you don't have a pH meter or the know-how to use one properly, you can use indicator papers, which are inexpensive but deteriorate with storage. With a few "books" of indicator papers covering the range 3 to 8 you should be able to get a value accurate to the nearest 0.2 pH units.

I'm assuming that by "formalin" you mean the concentrated solution that is nominally 37-40% by weight of formaldehyde gas in water. Its pH falls with time.
For more information about formalin, see https://www.cambridge.org/core/services/aop-cambridge-core/content/view/911F1870567E2487D56A51140EB8EA17/S1551929500057060a.pdf/div-class-title-formaldehyde-formalin-paraformaldehyde-and-glutaraldehyde-what-they-are-and-what-they-do-div.pdf. <https://www.cambridge.org/core/services/aop-cambridge-core/content/view/911F1870567E2487D56A51140EB8EA17/S1551929500057060a.pdf/div-class-title-formaldehyde-formalin-paraformaldehyde-and-glutaraldehyde-what-they-are-and-what-they-do-div.pdf>  It's a free download, with >600 citations according to Google Scholar.

John Kiernan
Emeritus, UWO, London, Canada
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________________________________
From: Paula Sicurello via Histonet <histonet at lists.utsouthwestern.edu>
Sent: September 12, 2023 10:11 PM
To: HistoNet <histonet at lists.utsouthwestern.edu>
Subject: [Histonet] Formalin pH

Hello Histoteckies,
What are y'all doing regarding the CAP requirement to monitor the pH of formalin?
We buy tons and tons of the 5 gallon cubitainers and we are still debating over how to check the pH.

Looking forward to your replies.
Toodles!
Sincerely,

Paula Sicurello
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