The effect of the inner solution on the potential in neutral carrier electrodes is considered constant in theoretical discussions. Because simplifying assumptions are made when deriving the potential equation, the purpose of this study has been to find out whether the measuring range of a valinomycin potassium electrode could be extended by changing the activity of the inner reference solution. The measurements show that changing the concentration of the inner solution in the range 10−5M - 0.1 M(1 M for calibration) does not affect the calibration curve, selectivity or the anion interference.