In the Nernst eqution, the slope factor RT/nF contains the value of the ion charge n. It is a value with sign (+ or -). -RT /nF is -0.059 V/decade if n is positive and 0.059 V/decade if n is negative.
Cornel Radu Thank you very much for your answer. Since I am familiar with that fact, I am actually wondering is it possible to maintain positive slope for cations. Is there maybe some theory explaining limitations of Nernst equation?
The Nernst theory doesn't has such a limitation. You can't change a universal law.
But if you need, for practical purpose, to change the slope sign, you may reverse the connections of the voltmeter when you do the measurements (put COM of the voltmeter to ISE, not to REF.
Remember that a voltage value doesn't have a sign. But a potential value has sign.
Cornel Radu Thank you once again on your answer. So if I have positive slope, that actually means that my electrode is showing response for anions?
Yes, you understood the case. But also pay attention how the voltmeter is connected.
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