Nicolsky-Eisenmann equation

The Nicolsky-Eisenmann equation or its different varieties [6,7] give a theoretical background for the determinations. The equation was proposed originally for explaining the alkaline ion interferences (the alkaline error) observed in the case of pH-selective glass electrodes ... 

The Nicolsky-Eisenmann equation supposes that the response of the primary and the interfering ions is similar. It is generally not true. More complex equations, for example [8], can give better fitting to the experimental observations. 

In the equal activity (concentration) method, a vertical line is drawn in the dynamic range of the electrode response of the calibration graph. We read the j and 2 1" ues and get the A = j - 2 difference. From the simplified Nicolsky-Eisenmann equation, we obtain... 

Indexes just indicate that the AE is measured in mV and S in mV/decade units. In reality, however, the two calibration curves are not parallel. The Nicolsky-Eisenmann equation is not rigorously followed. Therefore, depending on where the horizontal or vertical lines are drawn, different selectivity coefficient values can be obtained with the separate solution methods. Therefore, it is recommended that the selectivity coefficient be measured in the range of the ionic concentration of the samples using mixed solution methods. 

---