Nathan E. Ballou

Characterization and separation of inorganic fine particles by capillary electrophoresis with an indifferent electrolyte system

The feasibility of using capillary electrophoresis to characterize and separate submicrometer- and micrometer-size metal oxide particles (e.g., TiO2, Al2O3, and Fe2O3) was investigated. The use of indifferent electrolyte solutions such as sodium nitrate solutions leads to an electrolyte system without specific surface adsorption of ions but with essentially only electrostatic interactions between electrolyte ions and the surface of metal oxide particles. This system permitted development of a two-site dissociation model that was then applied to a description of the electrophoretic mobility of metal oxide particles as a function of the pH of the indifferent electrolyte solution. The use of unbuffered solutions, along with the tendency of metal oxide particles to form aggregates, prohibits the accurate determination of the electrophoretic mobility. Therefore, only a general agreement between the predicted electrophoretic mobilities and the measured values was obtained using the model. Also, general agreement was achieved between the estimated isoelectric points for the metal oxides and the values reported in the literature. Furthermore, the optimum conditions for separating mixtures of metal oxide particles in indifferent electrolyte solutions were identified. Successful separations of different kinds of metal oxide particles and of metal oxide particles with different polymorphic forms were achieved.

Separation of micrometer-size oxide particles by capillary zone electrophoresis

Abstract High quality separations of three-component mixtures of suspended micrometer-size metal oxide particles have been achieved by capillary zone electrophoresis in two different high-pH aqueous buffer systems. Mixtures of Al 2 O 3 , Fe 3 O 4 and TiO 2 and of Al 2 O 3 , Fe 3 O 4 and Fe 2 O 3 were separated in 5–10 min in either carbonate buffer, pH 10.6 or pyrophosphate buffer, pH 10.2. The effects of electric field strength, buffer concentration and buffer type on separation quality were determined. Under optimized conditions, the separations were nearly baseline resolved. Complete separation of a mixture of Al 2 O 3 and UO 2 particles was also accomplished. Different sized particles/aggregates of a given oxide were found to co-migrate so that, for the systems studied, particle size effects were negligible and the separations were electrophoretic in nature. Reproducibilities of migration times and peak widths, heights and shapes were found to be excellent, with relative standard deviations of migration times consistently being

Separation and characterization of oxide particles by capillary electrophoresis

Separation of oxide particles by capillary electrophoresis (CE) is a relatively unexplored area. In environmental studies the ability to separate chemically different oxides by CE would permit characterization of the composition of mixtures of such particulate species and potentially could afford concentration enhancement or isolation of particular oxides from complex particulate matrices. Knowledge of the influence of different components of particle-suspending solutions on the surface characteristics of oxides assists in optimizing separations of particulate species. The effects of phosphate, carbonate, and borate anions and the sodium ion concentration on the electrophoretic mobility of titania, hematite, and alumina are investigated. All three anion types have significant effects on the electrophoretic mobility of each of the oxides, with borate anions yielding the highest degree of selectivity between titania and alumina. An Na+ concentration of 3 mM provides the best quality oxide separations for each of the buffer systems.

Electron Ionization Mass Spectrum of Tellurium Hexafluoride

The electron ionization mass spectrum of tellurium hexafluoride (TeF6) is reported for the first time. The starting material was produced by direct fluorination of Te metal or TeO2 with nitrogen trifluoride. Formation of TeF6 was confirmed through cryogenic capture of the tellurium fluorination product and analysis through Raman spectroscopy. The eight natural abundance isotopes were observed for each of the set of fragment ions: TeF5(+), TeF4(+) TeF3(+), TeF2(+), TeF1(+), and Te(+), Te2(+). A trend in increasing abundance was observed for the odd fluoride bearing ions, TeF1(+) < TeF3(+) < TeF5(+), and a decreasing abundance was observed for the even fragment series, Te(F0)(+) > TeF2(+) > TeF4(+) > TeF6(+), with the molecular ion TeF6(+) not observed at all. Density functional theory based electronic structure calculations were used to calculate optimized ground state geometries of these gas phase species, and their relative stabilities explain the trends in the data and the lack of observed signal for TeF6(+).

Selective fluorination and separation of metals with NF3 for mass spectrometry

We report recent progress on the development of a new methodology based on the generation of volatile metal fluorides through the use of nitrogen trifluoride (NF3) and the measurement of these metal fluorides by electron ionization mass spectrometry. Though unreactive under ambient conditions, NF3 reacts selectively at specified temperatures with various metal-containing species to form volatile metal fluorides. Utilizing these species-dependent traits, elements of a sample may be sequentially produced and thus separated on-line. Tellurium was reacted inside a thermogravimetric analyzer, the gas outlet of which was directly coupled to a quadrupole mass spectrometer with an electron impact ionization source.