A novel ion-selective electrode with membranes based on iron(III) phosphate and silver sulfide integrated into a completely new electrode body design has been developed for the determination of iron(III) cations. The best response characteristics with linear potential change were found in the iron(III) concentration range from 3.97 × 10-5 to 10-2 mol L-1. The detection limit was found to be 2.41 × 10-5 mol L-1 with a slope of -20.53 ± 0.63 and regression coefficient of 0.9925, while the quantification limit was 3.97 × 10-5 M. The potential change per concentration decade ranged from -13.59 ± 0.54 to -20.53 ± 1.56 for Electrode Body 1 (EB1) and from -17.28 ± 1.04 to -24 ± 1.87 for Electrode Body 2 (EB2), which is presented for the first time in this work. The prepared electrode has a long lifetime and the ability to detect changes in the concentration of iron cations within 20 s. Membrane M1 showed high recoveries in the determination of iron cations in iron(III) standard solutions (98.2-101.2%) as well as in two different pharmaceuticals (98.6-106.5%). This proves that this type of sensor is applicable in the determination of ferric cations in unknown samples, and the fact that all sensor parts are completely manufactured in our laboratory proves the simplicity of the method.
Keywords: ion-selective electrode; iron(III) cations; potentiometry.