Dear Tahir Ozkan,

Your question is a bit surprising. Why do you try to calibrate the silver electrode in the same way as you do it for the glass (H-sensitive) electrode? Do you really need to have the quantity pCl as a reading of pH meter or an outcome of your titrator? Hardly. The main purpose of your combined silver electrode is to make titrations and it does not require any calibration at all.

If you perform direct potentiometric measurement (not titration) and want to get concentration (more precisely, activity) of Cl- ion in solution, you really need calibration. As for many other potentiometric measurements, this is simply done with a usual calibration plot. Using several calibration solutions, a plot of potential E versus –lgc is constructed, usually by linear regression method, from which an unknown concentration is calculated. An important point is that all the calibration solutions should have the same ionic strength similar to that in the samples to be analyzed. Another common way of calibration is the standard addition method.

Best,

Rouvim Kadis

Dear Tahir,

Your silver/silver chloride reference electrode should not be calibrated at all to measure pH as Rouvim Kadis stated before. However, the electrode can be damaged at least in two ways: (i) if your sample solutions are aggressive to the reference electrode and (ii) if you don't store your combined electrode in its proper storage solution for too long. And if your reference electrode is damaged, your calibration would be poor.

Greetings,

Let me make a clarification. Tahir Ozkan asked a question about calibration of the (combined) silver electrode he was dealing with. This is an indicator electrode for halide titration (a silver rod in a silver-ion-containing solution), not the silver/silver chloride reference electrode that Ademario Junior is talking about, although the latter is of course part of the combination electrode.

Best,

Rouvim Kadis

Thank you, Rouvim Kadis . Maybe now I can understand the problem. If Tahir Ozkan is going to titrate with a silver ion indicator electrode, its autotitrator should read in millivolts rather than pH along with the titration itself. I believe the autotitrator must have this kind of option. The direct plot of mL x mV and its derivative should point to the titration final point.

However, if Tahir Ozkan also wants to verify the state of his Ag+ indicator electrode, he should perform a calibration curve with Ag+ standard solutions, but all of them should be prepared with the same total ionic strength.

To achieve this goal, the solvent for all standards must not be water but a saline solution with a high concentration of potassium nitrate, for example. I would advise 1,0 mol/L potassium nitrate solution and the standard with higher concentration should be [Ag+] = 0,0100 mol or less. Be careful with the potassium nitrate you choose since it must have the lowest chloride concentration as a contaminant you can find. And pour a few drops of nitric acid into the solvent solution to avoid Ag+ precipitation.

All solutions should be read in millivolts and the plot is - log [Ag+] x (mV readings). Since - log [Ag+] can be shortened to pAg, if this pAg x mV plot has an inclination around 53-59 mV/pAg, the electrode is ok.

I hope now I have been more helpful.