Ion selective electrodes for protonable nitrogen containing analytes: Metallacarboranes as active membrane components

Highlights: • ISEs based on simple and low cost polymer membranes for different bioactive nitrogen containing compounds were prepared. • The analytical parameters, life time, response time, slope, concentration range, limit of detection and selectivity are very favorable. • The proposed anion represents a good material for ISEs preparation used in clinical and pharmaceutical daily routine analysis. -- Abstract: Ion selective electrodes with simple electroactive membrane components have been prepared for the testing of dopamine, nicotinic acid, nicotinamide, histamine and metformin in aqueous solutions. The electroactive membrane component is the salt made of the protonated targeted analyte and the metallacarborane anion [Co(1,2-C2B9H11)2]−. The reason for the good performance of [Co(1,2-C2B9H11)2]− is its large capacity to produce weak hydrogen and dihydrogen bonds with the cation and the plasticizer that prevents leakage of the electroactive component. In this paper, we prove how easy is to produce a sensing material for a specific target. The only requirement is that the target has a protonable nitrogen, a situation encountered in many biological molecules or in many bio-relevant molecules. The analytical parameters for evaluation of ISEs performances, such as linearity range, slope, limit of detection, response time, and selectivity were studied and determined and all the produced selective ISEs have given favorable answer. The proposed electrodes showed Nernstian responses for protonable nitrogen containing analytes for almost 4 decades of concentrations, 1.00 × 10−6 to 1.00 × 10−2 mol dm−3, with fast response time (5 s) and adequate operational lifetime (50 days). For Dopamine the prepared ISEs exhibited linear responses with slope of ca. 58 mV decade−1 within the range 5.00 × 10−6 to 1.00 × 10−2 mol dm−3 and with a low detection limit of 1 μmol dm−3. The limits of detection ranged from 0.7 μmol dm−3 for nicotinamide up to 6 μmol dm−3 for metformin