Calcium-selective electrode based on polyaniline functionalized with bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate Original Research Article

A new Ca2+-selective polyaniline (PANI)-based membrane material suitable for all-solid-state sensor applications is presented. The membrane consists of electrically conducting PANI, bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphoric acid (DTMBP-PO4H), dioctyl phenylphosphonate (DOPP) and cationic (tridodecylmethylammonium chloride, TDMACl) or anionic (potassium tetrakis(4-chlorophenyl)borate, KTpClPB) lipophilic additives. PANI transforms the ionic response to an electronic signal and functions at the same time as the membrane matrix. PANI is made soluble in dichloro methane (DCM) with the Ca2+-selective DTMBP-PO4H ligand and membranes can easily be prepared by drop-casting on glassy carbon (GC) substrates. PANI membranes with three different plasticizer (z) and additive (s) contents were studied (the molar ratios between the plasticizer or additive and DTMBP-PO4H are denoted as z and s, respectively). The best electrode performance, considering sensitivity and selectivity, was obtained for PANI membranes prepared with z=0.90 and s=0.10, containing KTpClPB as ionic additive. The Ca2+-sensitivity of this membrane was 27.8±0.2 mV/log aCa2+ (10−1 to 10−4 M CaCl2, LOD=8×10−7 M) in 0.1 M NaCl, and the selectivity coefficients (log KCa,jpot) towards j=Na+, K+, Li+, NH4+ and Mg2+, determined with the fixed interference method, were −3.9±0.1, −4.0±0.1, −3.5±0.1, −3.5±0.1 and −3.6±0.1, respectively. On the other hand, practically no redox or pH sensitivity was observed when TDMACl was used as the ionic additive. The PANI membranes were characterized with potentiometry, electrochemical impedance spectroscopy (EIS) and UV–VIS.