I made 16% paraformaldehyde from scratch (dissolving powder in ddH20). While I was attempting to pH it, it would rapidly switch from alkaline to acidic according to the pH strips we use (range pH 6-10). I finally got it in the middle range (approx. pH7.8), so I filtered it and aliquoted it into 15ml conicals. The next day I checked the pH and it read at ~5.
I don't know what would cause this rapid change in pH overnight. I've done some reading on PFA cycling and I think maybe if I got it into the alkaline range it might be more stable but I'd really prefer for it to be at a physiological pH.
I'd appreciate any input on how to get to a physiological pH and how to keep it stable.
Formaldehyde is not very stable in solution; it is hard to competely dissolve PFA, and then it tends to precipitate in part if there are no stabilisers added. This is probably worse with 16% than with the usual 4%.
Is there a stabilizer you would recommend? I thought about trying it with PBS instead but I wasn't sure if that would change the pH issue.
Methanol is what is usually used in commercial solutions, at variable concentrations. I would suggest you look at commercially available formaldehyde, already diluted (37% is a commonly available concentration), and either use that for your work, or try to replicate what manufacturers include. I don't have any direct experience of making formaldehyde, much easier to buy it ready to use.
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