[dlow]

Hi all.

After a bit of help trying to understand what I am doing in work.

I have just switched labs and I am now analysing copper via an iodometric titration with thiosulfate.

I get the basic chemistry of what is going on but it’s the method of EP determination that I am puzzled on.

All the information I have found on the internet involves a starch indicator and a colour change. In work it is automated using metrohm equipment but the end point is determined potentiometrically. I know that metrohm offer an electrode that can detect a colour change but it is not used. Instead a thermo platinum combination ORP electrode is used.

Can anybody tell me why this approach is used and recommend any literature I can read up about it please?

Thanks in advance.


Dave

[chenbeier]

For automatic processes it is more easier to detect a voltage.  Every redox reaction create a electrical potential, calculated according Nernst.
For this reason it is also used for iodometric titration.
The same is measuring pH instead to use an indicator.

[dlow]

Hi chenbeier.

Thanks for the response. I thought it might have been something basic like that but I just wanted to double check just to make sure. I had doubt because I also titrate Pb with EDTA using Metrohm's Optrode which uses colour change and this is automated. Go figure!!

As a follow on question then to my original one (to which I think I know the answer but I am just making sure)..

Even though the end point is determined potentiometrically and not by a colour change. Should I still be cautious about the same interfering elements I am reading about in journals when the end point is the traditional colour change?

[Borek]

Every method of EP detection has its own quirks.

[dlow]

Hi Borek.

Thanks for the response.

Do you know of any literature out there that involves a potentiometric EP? I have had a good look on the internet but I haven’t found any regarding this specific type of titraton.

[Borek]

I doubt you will find anything on just this particular titration, it is in no way different from detecting the EP of any other potentiometric titration using ORP electrode.