Buffering Neutral Fixer
I'd like to mix a neutral rapid fixer, relatively low-odour, that can keep its pH about-neutral when used after a citric acid stop bath. I've researched APUG, and I can see many references to a buffered fixer by Ryuji, however, all of those referenced pages seem to have been deleted, and are not to be found elsewhere. I suppose there were reasons why that recipe was removed from APUG and from the public domain, which is why I am not posting those thread references, and I am not asking for it. The only Ryuji recipe for a neutral fixer is http://www.apug.org/forums/forum226/...pid-fixer.html, which is similar to the below one, MF-2, except it uses 5g sodium metabisulfite instead of boric acid, but it seems to me that it may not have much of a buffer. Other fixer discussions do not mention buffering much.
However, I found the following, somewhat alkaline, recipe MF-2 on Flickr:
Ammonium Thiosulfate - 120g (200mL of 60% solution)
Sodium Sulfite - 15g
Borax - 5g
Boric Acid - 5g
Water to make 1L (pH 8.0)
I remember reading somewhere that borax, triethanolamine, or disodium phosphate would make good buffers for a fixer, and I am aware of Ryuji's use of salicylic acid combined with triethanolamine as a buffer (and a chelating agent I think) for his developers.
I could go ahead and adjust the proportions of borax, metaborate, and either boric acid or sodium metabisulfite until I get pH of about 7, but I am concerned that in doing so I would not be making a good buffer, but just using up the buffering ability of such a mix to arrive at a desired pH, which sounds counterproductive to me. Do I need a quick lesson in pH 7 buffers suitable for fixers?
Could the collective chemical mind of APUG make a suggestion as to a sensible neutral buffer to use for an ammonium thiosulfate/sodium sulfite rapid fixer?
As an adjunct to this, I am curious about a buffer for a citric acid stop bath. I guess I do need a lesson in buffers.
Last edited by Rafal Lukawiecki; 03-10-2013 at 01:11 PM. Click to view previous post history.
Reason: Clarified grammar