Ion-selective electrodes (ISEs) are chemical sensors with the longest history, and still probably have the largest number of applications. 1 More recently, two types of potentiometric wiretype electrodes (WTEs), such as coated wire electrodes (CWEs) 2 and solid contact electrodes (SCEs), 3,4 have exhibited rapid development. In WTEs, a total elimination of the internal filling solution provides new advantages. Simplicity of design, lower costs, mechanical flexibility, the possibility of miniaturization and microfabrication has widened the applications for WTEs in the fields of medicine and biotechnology. In SCEs of these two advanced types of WTEs, after polymerization, these polymer-coated metal electrodes were dipped into a PVC cocktail membrane solution until a bead was formed. Especially, these SCEs based on the electropolymerization method of amino derivatives onto the metal surface produced very good results, such as stabilization of the base potential, reproducibility, best selectivity, wide response ranges and fast response time. 5,6 Thus, in recent years, there have been many reports on hydrogen ion-selective SCEs 7 and hydrogen ion-selective ionophores. 8 We have studied hydrogen ion-selective ionophores and SCEs in our laboratory.
9After Simon 10 published information about tridodecylamine ionophore for hydrogen sensing, we synthesized various types of tertiary amine compound ionophores, and strived to understand the response characteristics of these ionophores. [11][12][13][14][15] Particularly, after our result concerning SCE based on the tribenzylamine (TBA) ionophore 16 was published, which had a wider response range than the electrodes with tridodecylamine (TDDA) ionophore, many types of aromatic tertiary amine compound ionophores were synthesized and studied. [17][18][19][20][21] We found that the response ranges shifted to an alkali range (toward pH 14) by extending the chain length between the phenyl ring and nitrogen in the ionophores, and were able to synthesize ionophores that exhibited a linear response up to pH 14. 22 As can be seen in the various results published until now on aromatic and aliphatic ionophores, however, there have been no reports on ionophores that are particularly effective in a strong acidic solution.In the present work, amine compound ionophores that could respond linearly to strong acid were synthesized, which has been noted as a limit of SPM (solvent polymeric membrane) ionophores, [13][14][15][16][17][18][19][20][21][22] and response characteristic due to structural changes of the ionophores in strong acid were demonstrated. Especially, we examined the responses resulting from increasing numbers of phenyl rings in ionophores, which had not been previously studied. Additionally, other common pH response characteristics of all solid-state potentiometric sensors for hydrogen ion based on poly(aniline), covered with a plastic PVC membrane and activated by these ionophores, are presented and evaluated in terms of analytical applications, such as in artificial serum an...
