Related Experiment Video
Updated: May 18, 2026

Studying Surfactant Effects on Hydrate Crystallization at Oil-Water Interfaces Using a Low-Cost Integrated Modular Peltier Device
Published on: March 18, 2020
Surfactant self-assembling in the gas phase: bis(2-ethylhexyl)-sulfosuccinate divalent metal ion anionic aggregates
Gianluca Giorgi1, Leopoldo Ceraulo, Vincenzo Turco Liveri
1Dipartimento di Chimica, Università degli Studi di Siena, Via Aldo Moro I-53100 Siena, Italy. gianluca.giorgi@unisi.it
Rationale:
Investigation of fundamental aspects driving surfactant self-assembling and of the capability of including guest molecules or ions in their micellar aggregates is an exciting research field for theoretical and technological reasons. In this light, assembling and chelating properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) towards divalent metal ion chlorides have been investigated in the gas phase by electrospray ionization mass spectrometry in negative ion mode, tandem mass spectrometry and energy-resolved mass spectrometry.
Methods:
Water/methanol solutions of AOTNa and chloride salts of nickel, magnesium, calcium and manganese, with different AOTNa/metal salt ratios, were infused into the electrospray source of a LCQ DECA ion trap mass spectrometer, operating in negative ion mode, at a flow rate of 5 μL/min. Low energy collision-induced dissociations were carried out by using helium with collision energy in the range 1-5 eV.
Results:
A variety of negatively singly charged monometallated and mixed metal aggregates have been observed, some of which were able to incorporate the metal counter ion of the inorganic salt used. The stability of these aggregates was evaluated by energy-resolved mass spectrometry which showed, for the anions [AOTM(II)Cl(2)](-), a stability order Ca > Mn > Mg > Ni. Their decomposition pathways show the unusual formation of the radical anions [C(4)HO(6)SM(II)Cl](-•).
Conclusions:
This study shed some light on the assembling and chelating properties of AOT(-) towards divalent metal ions to form negatively charged assemblies, some of them incorporating the metal counter ion of the inorganic salt used. Differently from what was observed with positively charged AOT-M(II) aggregates, solvated species were not detectable. An exception to the even-electron rule was observed in the decomposition pathway of [AOTM(II)Cl(2)](-).
Related Concept Videos
Micelles
Surface Active Agents
Breathing
Formation of Complex Ions
Colloidal precipitates
Preparation and Reactions of Sulfides

