Highly selective thiourea-based bulk optode for determination of salicylate in spiked urine samples, Aspirin® and Aspocid®

Thiourea-based bulk optodes were prepared for the determination of salicylate in biological and pharmaceutical samples; these optodes were prepared by embedding the thiourea ionophore in a plasticized poly (vinyl chloride) impregnated with the chromoionophore ETH7075 (Ob) or ETH5294 (Od). The observed optical response was explained by the salicylate extraction into the polymer via Hydrogen bond formation and simultaneous protonation of the chromoionophores yielding the absorbance change at 525 or 665 nm for Ob or Od, respectively. The developed optodes exhibited very good selectivity for salicylate over most lipophilic anions and oxoanions that can form Hydrogen bond. For instance, the optical selectivity coefficients using Ob optode, logKSal,anionopt, were as follows: SO42−<−6; Benzoate−=−2.6; NO2−=−4.01, which were greatly enhanced in comparison with that obtained by the previous work. Both Ob and Od exhibited detection limits of 3.9 × 10−5 and 1.0 × 10−4 mol L−1 with 3 and 5 min response times, respectively, at pH 4.5 using acetate buffer with very good reversibility. The developed sensors were utilized successfully for the determination of salicylate in spiked urine samples, Aspirin® and Aspocid®.