Development of electrochemical sensors responding to biologically active substances

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The development and application of electrochemical sensors including ion-selective electrode continue to be an area of focues. In this study, we developed new organic ammonium ion-selective membrane elctrodes using phosphate esters as ionophores. For example, a hexylammonium ion-selective electrode was constructed using tris (2-ethylhexyl) phosphate (TEHP) as the ionophore and dioctyl phthalate as a membrane solvent in a poly (vinyl chloride) membrane matrix. The electrode exhibited a near-Nernstian response to hexylammonium in the concentration range from 2**10^<-4> to 1**10^<-1> M with a slope of 57 mV per concentration decade. The lower limit of detection was 2**10^<-5> M,was comparable to that of the electrode made from one of the amine ionophore, a calix [6] arene analog, reported previously. The interaction between the phosphate ester and hexylammonium was confirmed by ^1H-NMR spectroscopy.We also appliied ion-selective electrodes to monitor free drug levels in blood serum. For example, free disopyramide levels in serum were determined in situ using a disopyramide membrane electrode. The potentiometric method is advantageous because the free concentration of the drug in serum can be determined without sample preparation. The free disopyramide concentrations determined by potentiometry compared with those obtained by fluorescence polarization immunoassay afforded a linear correlation coefficient of 0.996.We described here only two results. Other results can be seen through references described in the back of this report.