title: Time-resolved analysis of hydrolytic aluminum species in the formation of the tridecamer using electrospray ionization mass spectrometry.
abstract: The time-resolved analysis of neutralized aluminum solution was conducted by electrospray ionization mass spectrometry (ESI-MS) for the speciation of aluminum. Using this technique, the behavior of each aluminum species in a 'short-term' (on the order of minutes) reaction time could be observed. Partially neutralized aluminum solutions (R = [OH(-)](add)/[Al(3+)](T) = 0-3) were adopted to elucidate the formation mechanisms of aluminum species, some of which are industrially and geochemically important. The behavior of the species in the solution at R = 1.5 was dependent on aging time for the first 24 h, while solutions at R = 0 and 3 were quickly equilibrated. At R = 1.5, the time lag for the gradual formation of aluminum tridecamer and the sudden decrease of monomer indicates the presence of an intermediate species: the pentamer. In the concentrated aluminum solution ([Al(3+)] = 1 mol/L) at R = 1.3, where the tridecamer was absent, the hexamer was observed instead of the tridecamer. This hexamer was decomposed to the monomer by dilution, and then the formation of the tridecamer was observed. Two reaction pathways exist for the formation of the hexamer and tridecamer, and the pentamer is proved to be a key to the formation of both the tridecamer and the hexamer. The tridecamer and hexamer, which are detected by nuclear magnetic resonance ((27)Al NMR) and potentiometric titration, respectively, were simultaneously observed by ESI-MS. This indicates that ESI-MS complements conventional techniques such as (27) Al NMR and potentiometric titration for the speciation of aluminum, and can offer detailed information on the dynamics of aluminum species.
authors.affiliation: Tokyo University of Marine Science and Technology, 4-5-7, Konan, Minato-ku, Tokyo 108-8477, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Urabe
authors.forename: Miho
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D006868:Hydrolysis; D019906:Nuclear Magnetic Resonance, Biomolecular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013997:Time Factors
chemical_list: D002412:Cations; D000535:Aluminum