Hello!
I am to titrate an aqueous solution of sulphides ( quantity - ppm ) with diaminosilver nitrate by using potentiometry. I use sulphide / silver and glass electrodes. Despite many various trials and changing parametres my measures are permanently unstable. What may cause the problem?
Thanks indeed.
You are trying to determine the content of the sulphide ion by the exchange reaction
[Ag(NH3)2]NO3 + Na2S = Ag2S + NH3 + NaNO3
And you are experiencing oxidation reactions of the ion sulphide
2S2- + H20 + 202 + S2032- + 20H-
2S2- + 2H20 + O2 = 2S + 40H-
See
https://core.ac.uk/download/pdf/11472029.pdf
Best regards.
Are you using the glass electrode as the reference? I'm guessing so.
The obvious source of problems is poor connexions in either the signal or shield for the electrodes. If the connexions are OK the next thing to check is whether the potential measuring equipment is designed to work with a high impedance reference input. Lastly, in high impedance circuits, grounding and electrostatic charge can cause problems depending on the design of the meter, and you may need a Faraday cage.
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