Experimental and Semiempirical Investigation of Interaction Between Fast Sm Membrane Sensor and 1, 3-Di(Thiophene Imino) Benzoic Acid

This work describes, for the first time, the theoretical modeling of structure and interaction between Sm³⁺ ion and 1, 3-di(thiophene imino)benzoic acid (DTBA) as a chelating reagent in the membrane and solution which were performed using the PM6/SPARKLE semiempirical method in the MOPAC program. Computational modeling results can be predicted behavior of Sm-DTBA interactions which was used as an ionophore for construction of samarium-selective potentiometric membrane sensor. The best performance was obtained with a membrane composition of 31% (w/w) PVC, 62% tributylphosphate (TBP), 4.8% DTBA and 3.2% sodium tetraphenyl borate (NaTBP). This sensor has a Nernstian slope of 19.6 mV decade for Sm³⁺ ions in the range of 1.0 × 10^-1 - 5.0 × 10⁶ M and the detection limit was 3.1 × 10^-6 M. The response time of the sensor is very fast (≤ 5 s) and the potentiometric response is independent of the pH of the solution in the pH range of 4.5-8.5. This sensor shows good selectivity for Sm³⁺ ion with respect to alkali, alkaline earth and heavy metal cations. The proposed sensor has been used for indirect determination of some drugs such as homatropine hydrobromide and hyoscine N-butylbromide in their pharmaceutical formulations and fluoride ions in mouthwash samples.