A novel Er(III) sensor based on a new hydrazone for the monitoring of Er(III) ions

N′-(2-Hydroxy-1,2-diphenylethylidene) benzohydrazide (HDEBH) was found to be a suitable neutral pseudo-ionophore for the preparation of a highly selective Er(III) membrane sensor. Poly vinyl chloride (PVC)-based membranes of HDEBH with potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as an anionic additive, and dibutyl phthalate (DBP), nitrobenzene (NB), and o-nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators were prepared and investigated as Er(III) sensors. A membrane composed of HDEBH-PVC-KTpClPB-DBP with the ratio 5.0:30.0:3.0:62.0 (0.015 mmol HDEBH–30 wt.% PVC–0.006 mmol additive–62% DBP) works well over a wide range (1.0 × 10−7 to 1.0 × 10−2 M) with a Nernstian slope of 21.0 ± 0.5 mV per decade of activity between pH values of 3.2 and 8.9. The detection limit of the sensor was calculated to be 7.0 × 10−8 M. The proposed electrode shows excellent discrimination toward Er(III) ions with regard to most common metal ions, and especially, all lanthanide ions (lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, holmium, thulium, ytterbium, lutetium). To test the analytical applicability of the sensor, it was successfully used as an indicator electrode for the titration of Er(III) ions with EDTA.