Preparation of Sodium Ion-Sensing Plates Based on a Thin Layer Liquid Membrane Containing a Neutral Ionophore and a Lipophilic Anionic Dye

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A sodium ion-sensing plate was prepared as an easily-handled ion-sensing optical chemical sensor (optode) probe. The sensing plate consisted of an ion-sensing liquid thin layer containing a Na⁺-selective neutral ionophore (16-crown-5 derivatives) and a lipophilic anionic dye (KD-A3), which was placed on a chemically modified (octadecyl silanized) frosted glass plate that was covered with a cellulose dialysis membrane. This ion-sensing plate can easily determine Na⁺ ranging from 10^-4 to 10^-1 M by simply dipping the plate into the sample solution. The response time was ca. 80 s for 10^-1 M NaCl with good reproducibility (relative standard deviation (RSD)=±1.33% for ten sequential measurements).