Effects of quantitative composition of the sensing phase in the response of ionophore-based optical sensors

[Display omitted] •Numerical simulations of analytical characteristics of bulk optodes are performed.•Effect of the composition in the optode span, range, sensitivity is evaluated.•Response curves with intermediate plateau are predicted and obtained experimentally.•Algorithms for the fine-tuning of the optode response are developed.•The simulations are verified with Na+- and K+-selective colorimetric optodes. The response characteristics of the optical chemical sensors (optodes), namely response range, response span and sensitivity are quantitatively related to the composition of the sensor phase for the first time. The dependence of the characteristics of ion-selective bulk optodes on the concentrations of the indicator, ionophore and ionic additive (ion-exchanger) are simulated numerically and experimentally verified with Na+- and K+-selective colorimetric optodes. It is shown how the response span, response range, median and sensitivity depend on the sensor membrane composition. Response curves with an intermediate plateau are predicted theoretically and obtained experimentally. It is shown that the inflection point in the response curve does not necessarily refers to α = 0.5. The results can be used for the fine tuning of the optical response of chemical sensors.