Quantitative Analysis of Holmium Ion by a Ho 3+ Ion‐Selective Sensor Based on a Symmetric Thio‐Schiff's Base

A poly(vinyl chloride) (PVC) membrane sensor for holmium ions was fabricated based on N ‐[( Z )‐1‐(2‐thienyl)‐ methylidene]‐ N ‐[4‐(4‐{[( Z )‐1‐(2‐thienyl)methylidene]amino} phenoxy)phenyl] amine (TPA) as a new ion carrier, acetophenon (AP) as plasticizing solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode shows a good selectivity towards Ho 3+ ions respect to other inorganic cations, including alkali, alkaline earth, transition and heavy metal ions. The constructed sensor displays a Nernstian behavior (19.5±0.3 mV/decade) over the concentration range of 1 . 0×10 −6 to 1 . 0×10 −2 mol·L −1 with the detection limit of the electrode being 4 . 6×10 −7 mol·L −1 and very short response time ( ca . 5 s). It has a useful working pH range of 3.2–9.8 for at least 8 weeks. The electrode was successfully applied as an indicator electrode for the potentiometric titration of a Ho 3+ solution with EDTA and holmium determination in some alloys. The proposed sensor accuracy was studied by the determination of Ho 3+ in mixtures of three different ions.