This work explores the interactions of cations with highly negatively charged solid/aqueous interfaces. Vibrational sum frequency spectroscopy (VSFS) was exploited to observe interfacial water structure on the surfaces of fused quartz and titanium dioxide (TiO 2 ) in the presence of nine chloride salts with different alkali, alkaline earth, and transition metal cations. The results showed prominent specific cation effects at low concentration. The cations followed a direct Hofmeister series. On quartz surfaces the series was: