All-solid-state calcium-selective electrode prepared of soluble electrically conducting polyaniline and di(2-ethylhexyl)phosphate with ETH1001 as neutral carrier

A new type of an all-solid-state PVC-free Ca2+-selective electrode is described. The electrode membrane is prepared of soluble electrically conducting polyaniline (PANI), di(2-ethylhexyl)phosphate (H+DEHP-) and Ca2+-ionophore ETH1001. The influence of an incorporated lipophilic salt, potassium tetrakis(4-chlorophenyl)borate (KB(ClPh)(4)), in the electrode membrane was also studied. The non-conducting form of PANI is made electrically conductive with H+DEHP-, which is also a complexing agent for Ca2+. PANI is then dissolved in tetrahydrofuran (THF) together with the other membrane components and electrode membranes are easily prepared in a single step on a glassy carbon (GC) substrate by solution-casting. An important role of PANI is also to facilitate the charge transfer at the substrate I membrane interface. It is shown that incorporation of ETH1001 and KB(ClPh)(4) improves the Ca2+-sensitivity of the electrodes studied. The best Ca2+-sensitivity, 28.6 +/- 1.1 mV/log a(Ca) (10(-1)-10(-3) M CaCl2) in 0.1 M NaCl, was obtained for an electrode membrane containing 40% (m/m) PANI, 30% (m/m) ETH1001 and 30% (m/m) KB(ClPh)(4). No redox sensitivity was observed for a PANI electrode membrane consisting of 30% ETH1001 and 5% KB(ClPh)(4) in a solution of 10 mM Fe(CN)(6)(3-/4-) with 10(-1)-10(-3) M CaCl2 as the ionic background. The selectivity coefficient (logK(Ca.j)(pot)) of this electrode is -1.8 +/- 0.1, -1.7 +/- 0.1, -1.7 +/- 0.1 and approximately -2 towards j = Na+, K+, Li+ and Mg2+, respectively. A model describing the working mechanism of the different PANI-based ion-selective electrodes is also presented. (C)2000 Elsevier Science B.V. All rights reserved.