Biogenic amine-sensitive membrane electrodes using the hydrogen bond-forming ability of solvent mediators

Solvent mediators with hydrogen bond-forming ability were applied for the construction of biogenic amine-sensitive membrane electrodes by combining them with a lipophilic ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate. Solvent mediators, such as thiophosphate esters with a P=S group, generally strengthened the response to organic ammonium ions including histamine, and markedly suppressed the responses to inorganic cations, such as Na+ and K+, suggesting that hydrogen bonding between the NH3+ group of organic ammonium ions and the negatively polarized sulfur atom in the P=S group would enhance such responses. The response to serotonin was especially strengthened in the case of phosphate or thiophosphate esters with a P=O group. The alcoholic solvent mediator, 1-decanol, which has a similar hydrogen bond-forming ability, did not show a pronounced enhancing effect toward organic ammonium ions, while the phenolic mediator p-dodecylphenol exhibited a significantly high degree of selectivity toward histamine. The present results showed that many hydrogen-bonding solvent mediators have the ability to enhance the response to organic ammonium ions, and are thus also suitable for constructing biogenic amine-sensitive electrodes.