Potentiometric Sensing of Nonsteroidal Painkillers by Acyclic Squaramide Ionophores.

We report here a small library of a new type of acyclic squaramide receptors ( L1 - L5 ) as selective ionophores for the detection of ketoprofen and naproxen anions (KF - and NS - , respectively) in aqueous media. 1 H NMR binding studies show a high affinity of these squaramide receptors toward KF - and NS - , suggesting the formation of H-bonds between the two guests and the receptors through indole and -NH groups. Compounds L1 - L5 have been tested as ionophores for the detection of KF - and NS - inside solvent PVC-based polymeric membranes. The optimal membrane compositions were established through the careful variation of the ligand/tridodecylmethylammonium chloride (TDMACl) anion-exchanger ratio. All of the tested acyclic squaramide receptors L1 - L5 have high affinity toward KF - and NS - and anti-Hofmeister selectivity, with L4 and L5 showing the highest sensitivity and selectivity to NS - . The utility of the developed sensors for a high precision detection of KF - in pharmaceutical compositions with low relative errors of analysis (RSD, 0.99-1.4%) and recoveries, R %, in the range 95.1-111.8% has been demonstrated. Additionally, the chemometric approach has been involved to effectively discriminate between the structurally very similar KF - and NS - , and the possibility of detecting these analytes at concentrations as low as 0.07 μM with R 2 of 0.947 and at 0.15 μM with R 2 of 0.919 for NS - and KF - , respectively, was shown.