(K2IrCl6) were purchased from Sigma–Aldrich
(St. Louis, MO). Ten millimolar (10 mM) stock solutions of the analytes
were prepared in HClO4, and were diluted daily to the desired
concentration in Tris-buffer (15 mM tris(hydroxymethyl)aminomethane,
3.25 mM KCl, 140 mM NaCl, 1.2 mM CaCl2, 1.25 mM NaH2PO4, 1.2 mM MgCl2, and 2.0 mM Na2SO4, with the pH adjusted to 7.4).