Assessing ion-exchange properties and purity of lipophilic electrolytes by potentiometry and spectrophotometry

作者：Silvester Debbie S; Grygolowicz Pawlak Ewa; Bakker Eric^*

来源：Electrochemistry Communications, 2010, 12(1): 110-113.

DOI：10.1016/j.elecom.2009.10.048

• ETH 500
• Potentiometry
• Ionic liquid purity
• Inert lipophilic electrolyte purity
• Nile Blue
• Spectrophotometry

Many ionic salts synthesized using metathesis are often found to contain significant amounts of impurities, despite careful control of the weighing of starting materials. In this work, a potentiometric method is devised to monitor ion-exchange properties (or 'purity') of an organic solvent containing a lipophilic electrolyte. Its permselective behaviour is monitored by treating the solvent as a liquid membrane and contacting it with two aqueous solutions with different electrolyte activities. This electrolyte mismatch results in a drastic potential change when excess lipophilic cation-exchanger is titrated with anion-exchanger, altering the membrane from being cation to anion responsive. Here, the cation-exchanger potassium tetrakis(4-chlorophenyl)borate (KTpCIPB) dissolved in nitrobenzene was titrated with tetradodecylammonium chloride (TDDACl), in contact with Ag/AgCl electrodes placed in aqueous 1 M and 10(-2) M KCl, respectively. The predicted potential change of -214 mV was observed at the equivalence point, forming the inert lipophilic electrolyte ETH 500, in a very small concentration range of added anion-exchanger (0.8% for +/- 10 mV), suggesting good precision. The approach was confirmed by monitoring absorbance and fluorescence intensity changes of the chromoionophore Nile Blue. This method may be applied for the synthesis of a range of highly lipophilic salts for which established metathesis protocols are not suitable.

• 出版日期2010-1