Aqueous solutions were prepared by dissolving salts and acids in distilled and deionized water. Standard solutions of fixed pH value were prepared by dissolving citric acid (POCH, Gliwice, Poland) and boric acid (POCH). The buffer solution of 1 mM citric acid and 1 mM boric acid was titrated with 1M sodium hydroxide and 1M hydrochloric acid. NaOH (POCH) and HCl (POCH) were added to meet the desired pH value that is 4-12 and 2-3, respectively. All chemicals used for solution preparation were of analytical grade and were used as received without any further purification.
Designed pH sensors are ion-selective electrodes characterized by a sandwich structure with ion-selective membrane placed on the solid-contact layer. The solid-contact layer consisted of hydrous iridium dioxide (hIrO2) (Alfa Aesar, Haverhill, MA, USA), multiwalled carbon nanotubes (NTs) (Nanostructured & Amorphous Materials, Inc., Houston, TX, USA), and Poly(3- octylthiophene-2,5-diyl) (POT) (Sigma Aldrich, St. Louis, MO, USA). The ion-selective membrane consisted of hydrogen ionophore V (Calix[4]-aza-crown), sodium tetrakis(4-fluorophenyl)borate dihydrate, 2-Nitrophenyl octyl ether (NPOE), and poly(vinyl chloride) (PVC) of high molecular weight were purchased from Sigma-Aldrich. Dimethylformamide (DMF) and Tetrahydrofuran (THF) used as solvents were also purchased from Sigma-Aldrich.
Designed pH sensors are ion-selective electrodes characterized by a sandwich structure with ion-selective membrane placed on the solid-contact layer. The solid-contact layer consisted of hydrous iridium dioxide (hIrO2) (Alfa Aesar, Haverhill, MA, USA), multiwalled carbon nanotubes (NTs) (Nanostructured & Amorphous Materials, Inc., Houston, TX, USA), and Poly(3- octylthiophene-2,5-diyl) (POT) (Sigma Aldrich, St. Louis, MO, USA). The ion-selective membrane consisted of hydrogen ionophore V (Calix[4]-aza-crown), sodium tetrakis(4-fluorophenyl)borate dihydrate, 2-Nitrophenyl octyl ether (NPOE), and poly(vinyl chloride) (PVC) of high molecular weight were purchased from Sigma-Aldrich. Dimethylformamide (DMF) and Tetrahydrofuran (THF) used as solvents were also purchased from Sigma-Aldrich.