In our previous work, we determined a phase shift (Δ𝜑 &$' ) of 29.7 ± 0.7° for the pristine fused silica/water interface for hemispheres that were first exposed to ultrapure water (2 μΜ) at The SHG amplitude (Fig. ) is similar for both sulfate salts regardless of the cation identity. The SHG phase shifts relative to pure water (Figure ) across both sulfate and chloride species are approximately 30 o for all four salts surveyed. tot and χ Across the Cations. Our recent report shows a possible method of separating the second-and third-order contributions to the SHG signal and therefore estimating interfacial structure and potential using eqn. 2, 20 resulting in eqns. 3 and 4. We now use this method to determine how the second order nonlinear susceptibility (χ ) and the total surface potential, F(0)tot, depend on the chemical identity of the adsorbed ions and their concentrations.