DOI: 10.1002/elan.201400494 Solid-Contact Potentiometric Sensor Based on Polyaniline and Unsubstituted Pillar[5]Arene Ekaterina E. Stoikova, [a] Michail I. Sorvin, [a] Dmitry N. Shurpik, [b] Herman C. Budnikov, [a] Ivan I. Stoikov, [b] and Gennady A. Evtugyn* [a] 1 Introduction The development of potentiometric sensors with the solid contact eliminating internal filling solution has found in- creasing attention in the past decade due to simple design, durability, miniaturization prospects and low-cost manufacture [1]. In conventional ion-selective electrodes the membrane containing ionophore contacts with the inner reference electrode via solution with a constant concentration of a primary ion. Leaching of the internal solution and low mechanical robustness of the plastic membrane are considered as a weak point of such an as- sembly. Direct contact of the membrane with the electric contact requires implementation of the materials with mixed electronic and ionic conductivity which serve as ion-to-electron transducers. Besides oxides and complexes of transient metals, conducting polymers are intensively applied in solid-contact potentiometric devices. PANI, polypyrrole and polythiophene derivatives are described in the assembly of the solid-contact sensors for the detec- tion of alkali and alkali-earth metals [2–5], transient metals [6–9], inorganic anions [10, 11] and charged organ- ic species [12]. The electropolymerized layers in solid-contact poten- tiometric sensors are often covered with conventional PVC membranes containing plasticizer, lipophilic salt and ionophore. Meanwhile the mass and ratio of components of such membranes can differ from those applied in the sensors with internal filling. In some cases, lipophilic salts can be excluded because of the ion exchange properties of conductive polymer [9]. For PANI based sensors, chemically synthesized polymer is also used in addition to electropolymerization product. Although the electropoly- merized PANI forms thinner regular films, chemically synthesized material has higher purity and extended doping abilities. This eliminates drawbacks of PANI ap- plication, e.g., pH sensitivity of the potential and swelling with pH shift [9, 10]. On the other hand, conductive poly- mers do not show well defined redox potential and in some cases demonstrate slow conformational changes caused by redox transformations. This can result in hyste- resis phenomena observed for current À voltage functions and relaxation properties [13]. The morphology of the films and their penetrability for ions depend on the fabri- cation protocol, nature of a counter ion and storage con- ditions [14, 15]. This complicates the fabrication of solid- contact sensors because of insufficient reproducibility and long-term drift of their potential. The behavior of poten- tiometric sensors based on electropolymerized materials exerting mixed potential with protonation and complexa- tion stages was considered in [16, 17] and the conditions for extracting ion-exchange contribution established. Pillar[5]arene (Scheme 1) is a representative of a new class of macrocyclic molecules that is made up of hydro- [a] E. E. Stoikova, M. I. Sorvin, H. C. Budnikov, G. A. Evtugyn Analytical Chemistry Department of Kazan Federal University 18 Kremlevskaya Street, Kazan, 420008, Russian Federation *e-mail: Gennady.Evtugyn@kpfu.ru [b] D. N. Shurpik, I. I. Stoikov Organic Chemistry Department of Kazan Federal University 18 Kremlevskaya Street, Kazan, 420008, Russian Federation Abstract : A novel potentiometric sensor based on screen- printed carbon electrode covered with electropolymerized polyaniline (PANI) and unsubstituted pillar[5]arene as ionophore has been developed and tested in potentiomet- ric measurements of pH and metal ions. The introduction of pillar[5]arene improved the reversibility of the pH re- sponse in the range from 2.0 to 9.0 with the slope of 45 mV/pH. Among metal cations, the response to Fe 3 + and Ag + ions was referred to PANI redox conversion whereas the signal toward Cu 2 + in the range from 1.0  10 À6 to 1.0  10 À2 M (limit of detection (LOD) 3.0  10 À7 M) to specific interaction with the macrocycle. Keywords: Potentiometric sensor · Solid-contact sensor · Pillar[5]arene · Polyaniline · Electropolymerization Scheme 1. Structure of Pillar[5]arene. www.electroanalysis.wiley-vch.de  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2015, 27, 440 – 449 440 Full Paper