[dlow]

Hello I'm performing quantitative analysis of silver at the moment in work. I am determining the end point potentiometrically.

I like to know the chemistry behind things I do so I have been doing a bit of background reading and research.

Certain silver nitrate solutions that I produce have a yellow tint to them, which indicates palladium present. I have to precipitate the palladium out of solution using DMG because palladium stops the titration end point from being detected.

Does anybody know how/why palladium does this? I can't seem to find this information.

I look forward to your responses.

[Borek]

What kind of titration, what kind of electrode?

Not that I have any ideas, but without more detailed information it is difficult to even start thinking.

[dlow]

I have used two combination electrodes. Metrohm's Ag Titrode and Thermo-Scientific's Silver Sulphide  electrode. I use KBr as my titrant.

But to be honest I don't think it really matters. This is an industry standard method that my company has employed for years but as time has gone by the chemistry behind the method has dwindled and existing staff cannot tell me why. They just know it does and thats why we need to use DMG.

[Arkcon]

So the sample is yellow, not black as I'd guess a finely divided metal would look.  (Sometimes they don't but back is typical.)  So maybe its a palladium salt of some sort?  I'm guessing it will compete for the reaction your KBr is supposed to undergo with silver ions in solution?

[Borek]

There are four quite stable PdBr_n complexes (logKf 5.17, 9.42, 12.7, 14.9), if Pd²⁺ is left in the solution you will probably determine some sum of Ag⁺ and Pd²⁺. I don't have time to calculate details right now, but interference seems obvious.