A New Neutral Carrier for Silver Ions Based on a Bis(Thiothiazole) Derivative and its Evaluation in Membrane Electrodes

摘要

Membrane electrodes based on 2,2'-dithio-bis(benzothiazole),DTBBT,as a neutral carrier for silver ions are described.Silver-selective membrane electrodes formulated with 2 wt% DTBBT ionophore and 50mol% TFPB in an FPNPE plasticized poly (vinyl chloride) exhibited near-Nernstian responses towards silver ions (60.3+-0.5 mV decade~(-1)) over a wide silver ion activity range of 0.83muM to 94 mM.Increasing the amount of anionic sites,TFPB,to 100 or 150 mol% (relative to the DTBBT weight) resulted in super-Nernstian responses toward silver ions.Membrane electrodes prepared using a low dielectric constant plasticizer,however,exhibited sub-Nernstian responses.Polymer membrane electrodes with optimal composition (i.e.,2wt% DTBBT,50mol% TFPB in FPNPE plasticized poly(vinyl chloride)) exhibited high potentiometric selectivity towards silver ions over alkali,alkaline earth,transition metal ions,as well as heavy metal ions such as Hg~(2+) and Pb~(2+).A good correlation was found between the potentiometric selectivity coefficients and the change in the UV-visible spectra of the ionophore upon exposure to different metal ions.The overall performance of the silver-selective membrane electrodes based on DTBBT ionophore,which is available at low cost,was found to be comparable to the performance of silver electrodes prepared with Fluka silver ionophore-IV.A DTBBT-based silver electrode was used as an indicator electrode for titrations of silver ions using standard sodium chloride solutions.Sharp inflections occur at the end point,and the data obtained showed 99.4% recovery with a standard deviation of 0.7% (n=3).In addition,the applicability of the DTBBT-based silver-selective electrode is illustrated by measuring the silver concentrations in natural water spiked with silver nitrate and by analyzing the silver in electroplating wastewater samples.The results obtained utilizing a DTBBT-based silver electrode showed very good agreement with the standard methods of analysis.