Nitrate salts

The AgNO₃ (99.8%), Co(NO₃)₂·6H₂O (99.0%), Cu(NO₃)₂·3H₂O (99.5%), Ni(NO₃)₂·6H₂O (99.0%), Pb(NO₃)₂ (99.5%) nitrate salts were purchased from Merck, Zn(NO₃)₂·6H₂O (98.0%) and Cd(NO₃)₂·4H₂O (98.0%) were purchased from Aldrich. For preparation of PTC, phosphorus pentachloride (98%), trifluoroacetamide (97%), benzylamine (99%) and formic acid (97%) were used. Reagent grade chloroform (99.4%), dichloromethane (99.8%), 1,2-dichloroethane (99.8%) and nitrobenzene (99%) were tested as organic phases from Merck company; all chemicals were of the highest purity available and used without further purification. Doubly distilled deionized water was used throughout all experiments.

All the commercial-grade chemicals and reagents and all organic solvents were purchased from Sigma-Aldrich company and were used without further purifications. Stock solutions of all metal ions were prepared using their nitrate salts purchasing from Merck company. Also, Stock solutions of all anions were prepared using their sodium salts purchasing from Merck company. All the UV-Vis absorption spectra were recorded on Analytik Jena Specord S600 Spectrophotometer using a 10 mm path length quartz cuvette.

Ionophores were synthesized using aniline, 4-nitroaniline, resorcinol, ethyl acetoacetate, sulfuric acid, ethyl bromoacetate, potassium carbonate, acetone, hydrazine hydrate, ethanol, tetrahydrofuran (THF), and copper chloride purchased from Sigma-Aldrich. Graphite powder with particle size < 20 μm from Fluka and high-purity paraffin oil and multi-walled carbon nanotubes from Sigma-Aldrich were used to prepare carbon pastes. Potassium dichromate, sodium thiosulfate, and nitrate salts of the used cations (from Merck and Sigma-Aldrich) were of the highest available purity. Double distilled deionized water was used during the experiment.