AnsweredAssumed Answered

Trying to understand redox indicators

Question asked by Jason Kabanas on Sep 4, 2018
Latest reply on Sep 5, 2018 by Steven Cooke

Hi There,

My previous question didn’t attract any responses, so I’m going to try and rephrase the question. Im trying to learn about pH indicators to use in a product I’d like to develope, but I’m afraid my understanding of chemistry is making it difficult for me.


im looking for some kind of pH indicator that can be added to an organic solvent, or even water, that will react to oxygen when later exposed. I’ve read about redox indicators but these seem to revert to their reduced form over time, where as I’m trying to find a type of indicator can be added and activate once and permanently. The reaction has to be instant, or near to. Ideally, I’d like for it to be naturally clear in its reduced form, just off of Wikipedia these compounds work as redox agents but I know nothing about their use or viability:


2,2'-bipyridine (Ru complex)+1.33colorlessyellow
Nitrophenanthroline (Fe complex)+1.25cyanred
N-Phenylanthranilic acid+1.08violet-redcolorless
1,10-Phenanthroline iron(II) sulfate complex (Ferroin)+1.06cyanred
2,2`-Bipyridine (Fe complex)+0.97cyanred
5,6-Dimethylphenanthroline (Fe complex)+0.97yellow-greenred
Sodium diphenylamine sulfonate+0.84red-violetcolorless
Sodium 2,6-Dibromophenol-indophenol

or Sodium 2,6-Dichlorophenol-indophenol

Sodium o-Cresol indophenol+0.62+0.19bluecolorless
Thionine (syn. Lauth's violet)+0.56+0.06violetcolorless
Methylene blue+0.53+0.01[2]bluecolorless
Indigotetrasulfonic acid+0.37-0.05bluecolorless
Indigotrisulfonic acid+0.33-0.08bluecolorless
Indigo carmine

(syn. Indigodisulfonic acid

Indigomono sulfonic acid+0.26-0.16bluecolorless
Safranin T+0.24-0.29red-violetcolorless
Neutral red+0.24-0.33redcolorless


What is the difference between pH independent and dependent?


Ive also learned that once these solutions “set” they will no longer function — does that mean they won’t revert back to a reduced state or that they will permenantly stay in their oxidized state?


Thank you, I look forward to any and all responses.