La3+ and Y3+ interactions with the carboxylic acid moiety at the liquid/vapor interface: Identification of binding complexes, charge reversal, and detection limits

Research output: Contribution to journalResearch articleContributedpeer-review


  • Adrien Sthoer - , KTH Royal Institute of Technology (Author)
  • Ellen M. Adams - , Ohio State University (Author)
  • Sanghamitra Sengupta - , KTH Royal Institute of Technology (Author)
  • Robert W. Corkery - , KTH Royal Institute of Technology (Author)
  • Heather C. Allen - , Ohio State University (Author)
  • Eric C. Tyrode - , KTH Royal Institute of Technology (Author)


Specific interactions of yttrium and lanthanum ions with a fatty acid Langmuir monolayer were investigated using vibrational sum frequency spectroscopy. The trivalent ions were shown to interact with the charged form of the carboxylic acid group from nanomolar concentrations (<300 nM). Analysis of the spectral features from both the symmetric and the asymmetric carboxylate modes reveals the presence of at least three distinct coordination structures linked to specific binding configurations. Although the same species were identified for both La3+ and Y3+, they display a different concentration dependence, highlighting the ion-specificity of the interaction. From the analysis of the response of interfacial water molecules, the reversal of the surface charge, as well as the formation of yttrium hydroxide complexes, were detected upon increasing the amount of salt in solution. The binding interaction and kinetics of absorption are sensitive to the solution pH, showing a distinct ion speciation in the interfacial region when compared to the bulk. Changing the subphase pH or adding a monovalent background electrolyte that promotes deprotonation of the carboxylic acid headgroup could further improve the detection limit of La3+ and Y3+ to concentrations < 100 nM. These findings demonstrate that nM concentrations of trace metals contaminants, typically found on monovalent salts, can significantly influence the binding structure and kinetics in Langmuir monolayers.


Original languageEnglish
Pages (from-to)2169-2180
Number of pages12
JournalJournal of colloid and interface science
Issue numberPt 2
Publication statusPublished - 15 Nov 2021
Externally publishedYes

External IDs

PubMed 34798383
ORCID /0000-0002-8120-8553/work/142251734



  • Arachidic acid, Carboxylate binding complexes, Carboxylic acid moiety, Charge reversal, Eicosanoic acid monolayer, Ion specific effects, Langmuir monolayer, Molecular characterization, Poisson Boltzmann theory, Trivalent ions, Vibrational spectroscopy, Vibrational sum frequency spectroscopy, Water, Limit of Detection, Vibration, Ions, Carboxylic Acids

Library keywords