N1,N2-Bis[1-(2-hydroxyphenyl)methylidene]ethanedihydrazide as a neutral ionophore for preparation of a new Ho3+ PVC-membrane sensor

N1,N2-Bis[1-(2-hydroxyphenyl)methylidene]ethanedihydrazide (MEH) was used as new compound which plays the role of an excellent ion carrier in the fabrication of a Ho(III) membrane electrode. The electrode shows a good selectivity for Ho(III) ion with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. This electrode has a wide linear dynamic range from 1.0 × 10−6 to 1.0 × 10−2 mol/L with a Nernstian slope of 19.8 ± 0.3 mV per decade and a low detection limit of 5.8 × 10−7 mol/L in the pH range of 2.5–9.8, while the response time was rapid (<10 s). The suggested sensor was applied to the determination of Ho(III) ions in tap water and river water samples.