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

Abstract

This work describes, for the first time, the theoretical modeling of structure and interaction between Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> 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 Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions in the range of 1.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> - 5.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> M and the detection limit was 3.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> 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 Sm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> 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.