Re: Is there a way of testing the strength of 10% formalin?

From:Barry Rittman <>

I would ask whether we really need to know the exact strength of the formaldehyde
solution? Most formalin stock solutions are around 37%-38% so that we are not really
getting a 10% formalin, 4% formaldehyde solution.
Most fixing solutions, including 10% NBF,  are used greatly  in excess of the strength
that is necessary to fix the tissue. Additionally, the amount of time that the tissue
is "fixed" in most laboratories really does not completely fix the tissue and the
fixation is therefore "completed" in the dehydration steps.
I'm sure that this will generate some comments.

"" wrote:

> Hello histonetters,
>         At our hospital laboratory the staff have been making up 10% formal saline
> for 40 years. An odd time one would come across a dud bottle of 38-40%
> formaldehyde and discard.
>         Recently however there has been a lot of dud bottles and I'm wondering is
> it the unseasonally cold spell of weather. The temperature in the Chemical
> store in the yard may have dropped well below (-7min.) the recommended
> 10-25C some nights and I'm wondering would this result in weak formalin.
>         There also is an uncharacteristic clear red tinge to blood stained
> specimens  as if it had a higher than usual alcohol content. (We decided
> not to change over to NBF years ago as it works fine for most Immunos. We
> are in the UKNeqas ICC and doing OK.
>         I thought even if the temp. dropped below 10C and subsequently was brought
> up to room temperature and diluted to make 10% formal saline then it would
> be fine. Does anyone have any experience of this kind of thing???
>         Any thoughts ?? I have asked the supplier for a "certificate of
> conformity" for this batch and the date of manufacture and it is pending.
> There is a use by date on it of Oct 2001. Is there a way of testing the
> strength of the formaldehyde or would a low pH indicate a deteriorating
> solution.
> Annette Ryan
> Medical Laboratory Technologist
> Histology Laboratory
> Our Lady of Lourdes Hospital
> Drogheda
> Co Louth

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