Experimental. The solutions are prepared using inorganic salts and HCl (Fisher Scientific, ACS Plus, Part # A144, 36.5-38.0%). Stock solutions of 1 M and 10 mM NaCl (Sigma-Aldrich, anhydrous, part # 746398, ≥99% pure)), MgCl2 (from MgCl2•6H2O, Sigma-Aldrich, part # M2670, ≥99.0% pure)), and AlCl3 (from AlCl3•6H2O, Alfa Aesar, part # 10622, 99.9995% pure) were prepared to obtain solutions with concentration ranges between 1 µM to 3 mM. This range was selected because the maximum Al 3+ concentration that can be used while maintaining a pH of about 4 is 3 mM. 1 M HCl was used to set the pH to 4 as needed. Conductivity (Thermo Scientific, Orion 4-cell I think)and pH (Thermo Scientific, Orion ROSS Ultra Triode, 8107UWMMD)values were determined regularly (Thermo Scientific, Orion Star A325, pH/conductivity meter). Only one salt is tested per day to prevent contamination at the interface from unwanted ions. is tested per day to prevent contamination at the interface from unwanted ions.