title: Polynuclear Speciation of Trivalent Cations near the Surface of an Electrolyte Solution.
abstract: Despite long-standing efforts, there is no agreed upon structural model for electrolyte solutions at air-liquid interfaces. We report the simultaneous detection of the near-surface and bulk coordination environments of a trivalent metal cation (europium) in an aqueous solution by use of X-ray absorption spectroscopy. Within the first few nanometers of the liquid surface, the cations exhibit oxygen coordination typical of inner-sphere hydration of an aquated Eu(3+) cation. Beyond that, outer-sphere ion-ion correlations are observed that are otherwise not present in the bulk electrolyte. The combination of near-surface and bulk sensitivities to probe metal ion speciation in electrolyte solutions is achieved by detecting electron-yield and X-ray fluorescence signals from an inverted pendant drop. The results provide new knowledge about the near-surface chemistry of aqueous solutions of relevance to aerosols and ion transport processes in chemical separations and biological systems.
authors.forename: Mrinal K
authors.initials: MK
authors.lastname: Bera
authors.forename: Mark R
authors.initials: MR
authors.lastname: Antonio
mesh_terms: D002412:Cations / Q000032:analysis / Q000737:chemistry; D005063:Europium / Q000032:analysis* / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D056928:X-Ray Absorption Spectroscopy / Q000295:instrumentation
chemical_list: D002412:Cations; D012996:Solutions; D005063:Europium