Determination of gadolinium(III) ions in soil and sediment samples by a novel gadolinium membrane sensor based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one Original Research Article

Highly selective and sensitive poly(vinyl chloride) (PVC) membrane electrodes based on 6-methyl-4-{[1-(2-thienyl)methylidene]amino}3-thioxo-3,4-dihydro-1,2,4-triazin-5-(2H)-one (MATDTO) as new carriers for gadolinium ion-selective electrode was reported. The membrane solutions containing PVC, o-nitrophenyl octyl ether (NPOE) as plasticizer, sodium tetraphenyl borate (NaTPB) as lipophilic ionic additive, and MATDTO, displays a calibration response for Gd3+ ions over a wide concentration range of 1.0 × 10−6–1.0 × 10−1 M with Nernstian slopes of 19.8 ± 0.2 mV per decade and a detection limit as 5.8 × 10−7 M. The sensor has a relatively fast response time of <10 s and can be used in the pH range 3.2–8.7 for at least 2 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for Gd(III) ions over a large number of interfering cations. The membrane sensor was used as an indicator electrode in the potentiometric titration of Gd(III) ions with EDTA. The proposed electrode was also applied to the determination of concentration of Gd(III) ions in soil and sediment samples and validation with CRMs.