Surface potential of β-alanine at the electrolyte/air and artificial seawater/air interface

Surface potential and surface tension measurements in the concentration gradient from 10−7 to 10−1 mol dm−3 of β-alanine in 10−4 mol dm−3 NaCl and in the artificial seawater of various salinities are done. Results show variations in the orientation of β-alanine molecules on the air/solution interface, depending on β-alanine concentration and salinity. For lower concentrations (below 2×10−3 mol dm−3) of β-alanine in NaCl solution and for lower salinities (below 8‰) the carboxylic group (COOH) is directed upward and the amino group (NH2) downward (toward the liquid bulk), while the opposite is found at higher salinities and higher concentrations of β-alanine. It is found, from the dependence of the effective dipole moment, μef on the concentration of β-alanine, that, in the concentration range below 10−3 mol dm−3, the dipole moment is simply related to 1/C. Above this concentration, the effective dipole moment is smaller and its value fluctuates.