More questions for chemists (or those more knowledgeable about chemistry than I):
1. Will DTPA-Na5 (or pure DTPA) dissolve in an organic solvent such as propylene glycol or TEA? All the structures in DTPA-Na5 are carbon-based, so I'm guessing it will be soluble, but I'm not sure. Would you suggest a version of DTPA other than the pentasodium salt?
2. Is there any advantage of using DTPA over HEDP (aka "Dequest 2010" and "Etidronic acid")? Kodak uses DTPA heavily, but perhaps that's because it behaves better in powder form? For a concentrate, I won't care about that. Perhaps HEDP would be more effective?
I discovered that my developers that use 45 g/L of sulfite do not form a precipitate when refrigerated (unlike XTOL). That suggests a more convenient usage: Mix it one litre at a time, and store in the refrigerator (labeled clearly!). It should last three times as long in the fridge, compared with storing at room-temperature of 20C. And six times as long in the fridge compared with room-temp of 30C. But storage means the Fenton reaction with iron will be a problem, hence my interest in chelating agents.