Application of 1-ethyl-3-(2,5-dihydro-4-(3,5-dimethyl-1H-pyrazol-4-yl)-5-oxo-1H-pyrazol-3-yl)thiourea as sensing material for construction of Tm3+-PVC membrane sensor

A thulium(III) membrane sensor was made using 2% sodium tetraphenyl borate (NaTPB), 65% dibutylphthalate (DBP), 30% poly(vinyl chloride) (PVC) and 3% 1-ethyl-3-(2,5-dihydro-4-(3,5-dimethyl-1H-pyrazol-4-yl)-5-oxo-1H-pyrazol-3-yl)thiourea (ET) as an ionophore. Conductometric study shows selectivity of the Et toward Tm3+ ions. Nernstian response of 19.6 ± 0.4 mV per decade of thulium concentration was observed, and the electrode worked well in concentration range of 1.0 × 10− 6 to 1.0 × 10− 2 mol L− 1 with a lower detection limit (LDL) of 7.2 × 10− 7 mol L− 1, in a pH range of 4.3–10.4. The selectivity of the sensor over alkaline, alkaline earth, transition and heavy metal ions was also found to be in a satisfactory range. To check the analytical applicability of the proposed Tm3+ sensor, it was successfully used as an indicator electrode in analysis of thulium in certified reference materials.

Research highlights
► This work reports development of polymeric membrane sensor for Tm3+ determination in certified reference materials.
► The novelty of this work is based on the high affinity of the ionophore toward the Tm3+ ions which causes the high selectivity of the sensor.
► The newly developed sensor is superior to the formerly reported Tm3+ sensors in terms of selectivity and detection limit.