Dear John

Probably, you PBS is doing its job, buffering the solution.  Try this:

Phosphate-bufferd formaldehyde.  Per 100ml:

70 ml distilled water
4 g paraformaldehyde ( we use the granular stuff sold by EMS because it's
easier to handle )
500 µl 1 N NaOH
Warm in a 60 °C waterbath for serveral minutes.
When everything is dissolved (usually < 5 minutes) add 30 ml 500 mM sodium
phosphate buffer at pH 7.4.
Filter.

We never had any problems with this during the past years.

Jacques


----- Original Message -----
From: "John C. Dennis" <dennijc@vetmed.auburn.edu>
To: "HistoNet Server" <HistoNet@pathology.swmed.edu>
Sent: Tuesday, May 23, 2000 10:33 PM
Subject: paraformalin again


> dear all
>
> A 4% paraform./PBS prep has gotten out of hand.  The paraformalin will not
> go into solution.  The pH is at least 10 (by ph paper).  Temp. is 65
> deg. C.
>
> I decided to use NaOH pellets this time.  I don't know why.  Normally, I
> use 10 N NaOH.  Never have I seen this problem.
>
> Any ideas?
>
> Does anyone know at what pH paraformalin goes into solution at between 60
> and 70 deg. C?
>
> As always, thanks for the help.
>
> John Carroll Dennis
> Anatomy, Physiology, and Pharmacology
> 109 Greene Hall
> Auburn University, AL  36849
>
>
>