What is the role of disodium phosphate in bleach recipes?

Discussion in 'Film and Processing' started by dan_lee|16, Apr 6, 2009.

  1. I was wondering what the role of disodium phosphate is in ferricyanide based bleaches? Every ferricyanide recipe I've seen has it... what can I substitute it with?
    (I live in Australia, but vanbar do not stock it, but they effin stock potassium dichromate! otherwise it'd be $3 for 500 grams like everything else from them)... Sigma Chemicals (Australia) want $50 for 500 grams and $80 shipping.. vanbar get a lot of their chemicals from here.. what a joke..
    Anyway, so I need to replace it.
    Vanbar sell EDTA tetrasodium salt and EDTA acid, not Ammonium Ferric EDTA, they also sell Ferric Ammonia Citrate, and Ferric Ammoniun Citrate, but I dont have a recipe for bleach from these.
    I'm left with Potassium Dichromate bleach (no way), and Copper Sulphate bleach (Acceptable as last result, but not keen on the alleged colour shifts compared to ferricyanide and edta bleaches).
     
  2. My unobtanium list so far:

    CD-3
    CD-4
    disodium phosphate
    Ferric Ammonium EDTA
    Phosphoric Acid
    Any phosphates
    Hydrobromic Acid
    Sodium Acetate (needed for the quinone bleach recipe.. hydroquinone is available cheaply here)
    quinone bleach recipe:
    Water 110-120F 800 ml
    Glacial acetic acid. 15 ml
    Sodium Acetate 3.5 g
    Potassium Sulphate 10.0 g
    Potassium Bromide 10 g
    Hydroquinone 0.75 g
    Copper sulfate pentahydrate 0.5 g
    Water to make 1 liter
    I can make sodium acetate easily (bicarb+vinegar, or acetic acid and sodium carbonate... all readily available).
     
  3. Disodium phosphate is a buffer to keep the pH stable. It can be replaced with trisodium phosphate and enough sulfuric acid to bring the pH down to the same level. If you are working without a pH meter, you can get close by calculating the number of moles of DSP and adding the same number of equivalents of H2SO4 (remember 2 equivalents per mole for this divalent acid).
    It should be possible to make ferric ammonium EDTA from ferric chloride, ammonium hydroxide, and tetrasodium EDTA, but please don't attempt this without a better reference than this note. There are very strong acid-base reactions involved here that could be dangerous if not handled correctly. I would not try this myself without more research.
    I once ordered some HBr while I was at Kodak. It cost something like $500 for 50 g (this was in 1980). It came in wax sealed glass bottles with dry argon instead of air. It was much cheaper to use NaBr and HCl.
     
  4. Unfortunately my source doesn't stock Ferric Chloride, though they sell Hydrochloric Acid, so I'd be able to synthesis it...though i dont want to get too complicated, looks like I'll be crossing off EDTA as a possibility.
    There are no phospates at all.. or phosphoric acid either.
    So I might be able to use sodium acetate in place of disodium phosphate, that, also not sold... but safe, quick and easy to make at home.
    edit: though I don know if that would just make the bleach less effective and neutralise stuff or not.. but its worth a try doing some tests
     
  5. should also be able to play with the acetic acid level.
     
  6. Not sure whereabouts in Oz you live but, in Adelaide we've got these guys.
    http://www.acechem.com.au/index.htm
    I normally ask the local pharmacist and he gets then over by truck for me. Most of the stuff you list they have on their list, but no idea what their price comparison is like.
    Cheers
     
  7. Cheers, I'm in NSW North Coast, and I'll ask the local chemist, he's a pretty good guy and my grandparents are in good with him, ive asked about stuff before i had a hard time tracking down for another project I was randomly interested in :)
     
  8. You must have very strict regulations on phosphates. Other common buffers are borate, carbonate, and acetate. I have no idea which of these will be stable in ferricyanide. I would proceed cautiously.
     
  9. sodium carbonate would react with the acetic acid and form sodium acetate anyway...
    So I think I may as well start with using sodium acetate... also not sold.. but easily made :)
     

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