Bare Metal Ions Research Articles

A Novel Molten Salt Mediated Synthesis of Mesoporous Metal Oxides with High Crystallization.

The controlled synthesis of mesoporous metal oxides remains a great challenge because the uncontrolled assembly process and high-temperature crystallization can easily destroy the mesostructure. Herein, we develop a facile, versatile, low-cost, and controllable molten salt assisted assembly strategy to synthesize mesoporous metal oxides (e.g., CeO2, ZrO2, SnO2, Li2TiO3) with high surface area (115-155 m2/g) and uniform mesopore size (3.0 nm). We find this molten salt mediated assembly enables the desolvation of the precursors and forms bare metal ions, enhances their coordination interaction with the surfactant, and promotes their assembly into a mesostructure. Furthermore, the molten salt assisted crystallization process can lower the collision probability of the target metal atom, inhibit its further growth into large crystals, and achieve a well-maintained mesostructure with high crystallization. Furthermore, this method can be expanded to synthesize various structured mesoporous metal oxides, including hollow spheres, nanotubes, and nanosheets by introducing the carbon template. The obtained mesoporous CeO2 microspheres loaded with Cu species exhibit excellent antibacterial performance and superior catalytic activity for the hydrogenation of nitrophenol with high conversion and cycling stability.

Possible Role of Metal-Ions in the Chemistry of Prochirality and the Origin of Chirality in the Interstellar Medium

Propylene oxide (c-C3H6O) is the first chiral molecule detected in the interstellar medium (ISM). Its recent detection has opened up newer avenues to be explored in interstellar chemistry. On earth, metal-ions play a preeminent role in the chemistry of chirality and prochirality. Taking a cue from this idea, we computationally investigate the possible role of metal-ions in (a) the origin of chirality in the ISM and (b) advancing interstellar prochiral chemistry; noting that prochirality is a severely understudied concept in astrochemistry. The gas-phase reactions of ethylene, and propylene with OOH radical to lead to the formation of ethylene oxide and propylene oxide respectively were noted to be excellent model reactions, and have been chosen to examine the role of the metal-ions. The interstellar metal-ions being studied (viz. Al+, Mg+, and Mg2+) are considered in three different forms─as bare metal-ions, or as hydrated metal-ions bound to one molecule of water, and as part of a neutral molecule. Carefully calibrated electronic structure calculations (CCSD(T) and DFT) were used to obtain the relevant saddle points (minimum energy structures and transition states). One key conclusion from this work is that, metal-ions, regardless of what form they are in, lead to the barrierless formation of the epoxides, thereby facilitating the generation of interstellar chirality. The key chemical, and astrochemical facets involved in the chemistry of metal-ions in the circumstellar envelope of IRC+10216 are also discussed herein in detail. This work further recommends the detection of four molecules in the ISM, namely, aziridine, methyl aziridine, 2-amino-3-hydroxy propane, and 2-hydroxy-3-amino propane. Lastly, a foremost point to emerge out of this study and related contemporary works probing the chemistry of metal-ions in the ISM is that metal-ions may act as the glue connecting interstellar gas-phase chemistry with the surface chemistry occurring on ice-grains, and could aid in the unravelling of complex and new aspects in astrochemistry.

Applications of polarizable continuum models to determine accurate solution-phase thermochemical values across a broad range of cation charge - the case of U(III-VI).

Contributing factors to the solution-phase correction to the free energy of the molecular clusters U(H2O)n(3+/4+) and UO2(H2O)m(1+/2+) (n = 8, 9, 30, 41, 77; m = 4, 5, 30, 41, 77) have been examined as a function of cavity type in the integrated-equation-formalism-protocol (IEF) and SMD polarizable continuum models (PCMs). It is observed that the free energy correction, Gcorr, does not smoothly converge to zero as the number of explicitly solvating water molecules approaches the bulk limit, and the convergence behavior varies significantly with cavity and model. The rates of convergence of the gas-phase hydration energy, ΔGhyd, wherein the bare metal ion is inserted into a molecular water cluster and ΔGcorr for the reaction exhibit wide variations as a function of ion charge, cavity, and model. This is the likely source of previously reported discrepancies in predicted free energies of solvation for metal ions when using different PCM cavities and/or models. The cancellation of errors in ΔGhyd and ΔGcorr is optimal for clusters consisting of only a second solvation shell of explicit water molecules (n = m = 30). The UFF cavity within IEF, in particular, exhibits the most consistent cancellation of errors when using a molecular cluster consisting of a second shell of solvating water for all oxidation states of uranium, leading to accurate free energies of solvation ΔGsolv for these species.

From Iron Pentacarbonyl to the Iron Ion by Imaging Photoelectron Photoion Coincidence

The dissociation dynamics of internal energy selected iron pentacarbonyl cations, Fe(CO)5(+), have been investigated using the imaging photoelectron photoion coincidence (iPEPICO) spectrometer at the Swiss Light Source. The molecular ion loses all five carbonyl ligands in sequential dissociations in the 8.5-20 eV photon energy range. The Fe(CO)5(+) parent ion is metastable at the onset of the first dissociation reaction on the time scale of the experiment. The slightly asymmetric and broad daughter ion time-of-flight distributions indicate parent ion lifetimes in the microsecond range, and are used to obtain an experimental dissociation rate curve. Further carbonyl losses were found to be fast at threshold. The fractional parent and daughter ion abundances as a function of the photon energy, that is, breakdown diagram, as well as the dissociation rates for the first CO loss were modeled using the statistical Rice-Ramsperger-Kassel-Marcus (RRKM) and statistical adiabatic channel model (SSACM) theories. The excess energy redistribution in the products was also taken into account in a statistical framework. The 0 K dissociative photoionization thresholds for the five carbonyl-loss channels were found to be 9.015 ± 0.024 eV, 10.199 ± 0.027 eV, 10.949 ± 0.033 eV, 12.282 ± 0.39 eV, and 13.821 ± 0.045 eV for the processes leading to Fe(CO)4(+), Fe(CO)3(+), Fe(CO)2(+), Fe(CO)(+), and Fe(+), respectively. The iron cation thermochemistry is well-known, and these onsets connect the bare metal ion to the other fragment ions as well as to the gas phase neutral Fe(CO)5.

Metal–Carbonyl Bond Energies in Phosphine Analogue Complexes of Co(CO)3NO by Photoelectron Photoion Coincidence Spectroscopy

Threshold photoelectron photoion coincidence spectroscopy was used to study a series of cobalt–organic complexes with phosphine and phosphine analogue ligands: PMe3Co(CO)2NO, PEt3Co(CO)2NO, AsMe3Co(CO)2NO, and SbMe3Co(CO)2NO. The two lowest energy dissociative photoionization channels were sequential carbonyl losses in all four cases. Nitrosyl loss was also observed as a minor channel from the molecular ion and as a major competitive dissociation from the first (carbonyl loss) daughter ion. Further sequential CO and NO losses lead to the LCo+ (L = PMe3, PEt3, AsMe3, SbMe3) ions, which, similarly to an earlier threshold collision-induced dissociation (TCID) mass spectrometry study on the phosphine complexes,(1) exhibited parallel ethene loss and methane loss dissociation reactions, although the bare metal ion was not observed. Unimolecular statistical rate theory (RRKM) calculations were performed to model the first two carbonyl loss channels and relate cobalt–carbonyl bond energy trends to the electron donor and acceptor properties of the phosphine analogue ligands. Co–CO bond energies of 0.90 ± 0.09, 0.84 ± 0.08, 1.13 ± 0.08, and 1.15 ± 0.09 eV were obtained in LCo(CO)2NO+ (L = PMe3, PEt3, AsMe3, SbMe3, respectively) and 0.82 ± 0.11, 0.74 ± 0.11, 0.95 ± 0.10, and 0.94 ± 0.09 in the first daughter ions, respectively.

Comparing the fragmentation chemistry of gas-phase adducts of poly(dimethylsiloxane) oligomers with metal and organic ions

Gas-phase ions of poly(dimethylsiloxane) oligomers were formed by electrospray ionization either by protonating them in solution with formic acid or by generating adducts of the oligomers with the metal ions Li+, Na+, K+, and Ag+ as well as with the organic cations NH4+, CH3CH2NH3+, and protonated glycine, aspartic acid, and 1,2-diphenylethylamine. The collision-induced fragmentation of the oligomeric ions was strongly dependent on the nature of the charging species. Ag+ adducts dissociated in a manner previously observed in secondary ion mass spectrometry experiments generating a series of linear and cyclic fragment ions, while Li+ adducts fragmented to form two ions: an adduct of the metal ion with the oligomer end-group and one with the remaining oligomer. Na+ and K+ adducts simply dissociate to form the bare metal ion. The organic species, to varying extents, transfer the proton to the oligomer to form a protonated poly(siloxane) ion. These protonated oligomers then dissociate at very low laboratory-frame collision energy along the siloxane backbone by loss of a silanol. These backbone fragments can then lose a methyl group to form a second series of fragment ions. Suggestions for probable mechanistic pathways for these processes are presented.

The dramatic effect of NH3co-ligation on the FE+-assisted activation of carbon dioxide in the gas phase: From bare metal ions to complexes

The catalytic efficiency of Fe(+) ion over the CO(2) decomposition in the gas phase has been extensively investigated with the help of electronic structure calculation methods. Potential-energy profiles for the activation process Fe(+) + CO(2) --> CO + FeO(+) along two rival potential reaction paths, namely the insertion and addition pathways, originating from the end-on kappa(1)-O and kappa(2)-O,O coordination modes of CO(2) with the metal ion, respectively, have been explored by DFT calculations. For each pathway the potential energy surfaces of the high-spin sextet (S = 5/2) and the intermediate-spin quartet (S = 3/2) spin-states have been explored. The complete energy reaction profile calculated by a combination of ab initio and density functional theory (DFT) computational techniques reveals a two-state reactivity, involving two spin inversions, for the decomposition process and accounts well for the experimentally observed inertness of bare Fe(+) ions towards CO(2) activation. Furthermore, the coordination of up to three extra ancillary NH(3) ligands with the Fe(+) metal ion has been explored and the geometric and energetic reaction profiles of the CO(2) activation processes Fe(+) + n x NH(3) + CO(2) --> [Fe(NH(3))(n)(CO(2))](+) --> [Fe(NH(3))(n)(O)(CO)](+) --> CO + [Fe(O)(NH(3))(n)](+) (n = 1, 2 or 3) have thoroughly been scrutinized for both the insertion and the addition mechanisms. Inter alia, the geometries and energies of the various states of the [Fe(NH(3))(n)(CO(2))](+) and [Fe(NH(3))(n)(O)(CO)](+) complexes are explored and compared. Finally, a detailed analysis of the coordination modes of CO(2) in the cationic [Fe(NH(3))(n)(CO(2))](+) (n = 0, 1, 2 and 3) complexes is presented.

Propane activation by MC 5H +5 (M = Ni and Co): An experimental and theoretical work

The reactions of MC 5H + 5 (M = Ni and Co) with propane in gaseous phase have been studied with an ion trap mass spectrometer; the MC 5H + 5 ions are able to activate the propane molecule which undergoes a dehydrogenation reaction. At variance with the reactions of the bare metal ions no loss of methane is observed; the reaction mechanism has been explored by means of DFT calculations and a possible explanation is offered for the different reactivity of these ligated ions.

Hydrated metal ions in the gas phase

Studying metal ion solvation, especially hydration, in the gas phase has developed into a field that is dominated by a tight interaction between experiment and theory. Since the studied species carry charge, mass spectrometry is an indispensable tool in all experiments. Whereas gas-phase coordination chemistry and reactions of bare metal ions are reasonably well understood, systems containing a larger number of solvent molecules are still difficult to understand. This review focuses on the rich chemistry of hydrated metal ions in the gas phase, covering coordination chemistry, charge separation in multiply charged systems, as well as intracluster and ion-molecule reactions. Key ideas of metal ion solvation in the gas phase are illustrated with rare-gas solvated metal ions.

Structural and Electronic Characterization of the Complexes Obtained by the Interaction between Bare and Hydrated First-Row Transition-Metal Ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and Glycine

The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.

Biophysical analyses of designed and selected mutants of protocatechuate 3,4-dioxygenase1.

The catechol dioxygenases allow a wide variety of bacteria to use aromatic compounds as carbon sources by catalyzing the key ring-opening step. These enzymes use specifically either catechol or protocatechuate (2,3-dihydroxybenozate) as their substrates; they use a bare metal ion as the sole cofactor. To learn how this family of metalloenzymes functions, a structural analysis of designed and selected mutants of these enzymes has been undertaken. Here we review the results of this analysis on the nonheme ferric iron intradiol dioxygenase protocatechuate 3,4-dioxygenase.

Gas-phase photoionization of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium(III)

In this Letter, we report observation of fragments of the metal–organic complex, Eu(2,2,6,6-tetramethyl-3,5-heptanedionato) 3 resulting from multiphoton ionization of the complex entrained in an Ar molecular beam. Photofragmentation was observed at 532, 355, 266 nm, and in the range of 460–466 nm. At each wavelength, the dominant fragments were bare metal ions in multiple oxidation states and ligand fragments. This fragmentation pattern is interpreted as resulting from excitation to ligand-to-metal charge-transfer states in the sequential ligand dissociation steps. Significantly weaker signal from EuO + and EuOH + fragments was also observed with photoionization at 266 nm.

The kinetic energy dependence of association reactions. A new thermokinetic method for large systems

The reactions of bare alkali metal ions (M+=Li+, Na+, or K+) with dimethoxyethane (CH3OCH2CH2OCH3, DXE) are studied using guided ion beam tandem mass spectrometry. The bimolecular reaction forms an associative M+(DXE) complex that is long-lived and dissociates back to the reactants. The kinetic energy dependences of the cross sections for formation of the complexes are interpreted with several different models (including rigorous phase space theory) that assume that the complex lifetimes are limited by dissociation over a loose, orbiting transition state. After accounting for the effects of multiple ion–molecule collisions, internal energy of the reactant ions, Doppler broadening, and dissociation lifetimes, the analyses yield 0 K bond energies as the only adjustable parameter. These values are compared with bond energies obtained from previous collision-induced dissociation (CID) studies of the M+(DXE) complexes and found to be self-consistent for all models studied. Association and CID form the same energized M+(DXE) complex in two distinct ways, such that a comparison of these results allows an assessment of the models used to interpret CID thresholds and test the limits of statistical theories such as RRKM and phase space theory.

Efficient polyatomic interference reduction in plasma-source mass spectrometry via collision induced dissociation

Evidence is provided that illustrates quadrupole ion traps can be used to selectively attenuate strongly bound diatomic ions occurring at the same nominal mass as an analyte ion of interest. Dissociation rates for TaO+ (D0 ∼ 750 kJ mol−1) are found to be at least an order of magnitude larger than the loss rate of Au+ due to scattering under “slow heating” resonance excitation conditions at qz = 0.67 and using neon as the bath gas. This rate difference is sufficient for the selective removal of this strongly-bound diatomic ion over the loss of the Au+ at the same mass-to-charge ratio. Other examples of quadrupole ion trap CID for the selective reduction of common plasma-generated species are also evaluated by examining the dissociation of GdO+ in the presence of Yb+, and Cu2+ in the presence of Te+. In each case, a different method of applying the excitation signals is presented, and the attenuation rates for the diatomic species due to CID are substantially larger than scattering losses for the bare metal ions. Evidence is also presented that demonstrates CID can be accomplished in concert with a slow mass analysis scan, thereby providing a means of (1) eliminating polyatomic ions (formed in the plasma or reaction cell) over an extended mass range, (2) recovering metal ion signal from the metal-containing polyatomic ions, and (3) minimizing deleterious secondary reactions of product ions.

Periodic Trends in Reactions of Benzene Clusters of Transition Metal Cations, M(C6H6)1,2+, with Molecular Oxygen

Mono- and bis-adducts of benzene of the type M(C6H6)1,2+ have been generated in the gas phase with first-, second-, and third-row transition metal cations, and their reactivities toward molecular oxygen have been measured using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Trends in reactivity were identified for the metal cation adducts across and down the periodic table. The intrinsic effect of the benzene ligand(s) on the reactivity of the bare metal cations was determined through comparisons with earlier results obtained for the bare metal ions. Molecular oxygen activation by early transition metal cations is preserved in the presence of one benzene ligand but almost disappears in the presence of two benzene molecules. The rate coefficients for O2 addition to late transition metal−benzene adducts are enhanced by up to 4 orders of magnitude in the presence of benzene. Thermochemical information is derived from the occurrence or absence of ligand-switching or ...

Reactions of atomic transition-metal ions with long-chain alkanes

Understanding metal ion interactions with long-chain alkanes not only is of fundamental importance in the areas of organometallic chemistry, surface chemistry, and catalysis, but also has significant implication in mass spectrometry method development for the analysis of polyethylene. Polyethylene represents one of the most challenging classes of polymers to be analyzed by mass spectrometry. In this work, reactions of several transition-metal ions including Cr +, Mn +, Fe +, Co +, Ni +, Cu +, and Ag + with long-chain alkanes, C 28H 58 and C 36H 74, are reported. A metal powder and the nonvolatile alkane are co-deposited onto a sample target of a laser desorption/ionization (LDI) time-of-flight mass spectrometer. The metal ions generated by LDI react with the vaporized alkane during desorption. It is found that all these metal ions can form adduct ions with the long-chain alkanes. Fe +, Co +, and Ni + produce in-source fragment ions resulting from dehydrogenation and dealkylation of the adduct ions. The post-source decay (PSD) spectra of the metal–alkane adduct ions are recorded. It is shown that PSD of Ag + alkane adduct ions produces bare metal ions only, suggesting weak binding between this metal ion and alkane. The PSD spectra of the Fe +, Co +, and Ni + alkane adduct ions display extensive fragmentation. Fragment ions are also observed in the PSD spectra of Cr +, Mn +, and Cu + alkane adduct ions. The high reactivity of Fe +, Co +, and Ni + is consistent with that observed in small alkane systems. The unusually high reactivity of Cr +, Mn +, and Cu + is rationalized by a reaction scheme where a long-chain alkane first forms a complex with a metal ion via ion/induced dipole interactions. If sufficient internal energy is gained during the complex formation, metal ions can be inserted into C–H and C–C bonds of the alkane, followed by fragmentation. The thermal energy of the neutral alkane is believed to be the main source of the internal energy acquired in the complex. Finally, the implication of this work on mass spectrometry method development for polyethylene analysis is discussed.

Experimental and Theoretical Studies of MCF3+ (M = Fe and Co): Reactivities, Structures, and Potential Energy Surface for C−F Activation

The gas-phase reactions of FeCF3+ and CoCF3+ with a series of small alkanes and alkenes were studied by Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. These ions, which are generated from the reactions of the bare metal ions with CF3I, both react with alkanes larger than ethane and with small alkenes primarily by CF2 displacement reactions. Hydride abstraction is also observed in some cases. Collision-induced dissociation and ion−molecule reactions indicate that the structure of MCF3+ ( M = Fe, Co) is an ion−dipole complex, FM+···F2C, involving C−F activation. A good fit of pseudo-first-order kinetics is obtained for the reactions of FeCF3+ and CoCF3+ with the above selected hydrocarbons. The reaction rates of FeCF3+ and CoCF3+ with the alkanes increase dramatically with the length of the alkane chain. The C−F activation mechanism of Fe+ or Co+ with the CF3 ligand was also investigated theoretically. The potential energy surface (PES) of the [Fe, C, F3]+ system and the local minima o...

The potential and challenges of elemental speciation by capillary electrophoresis-inductively coupled plasma mass spectrometry and electrospray or ion spray mass spectrometry

Capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) and electrospray (ES) or ion spray (IS) mass spectrometry (MS) are recently introduced techniques for elemental speciation. Both techniques have the potential for rapid elemental speciation with low detection limits. Examples of the use of CE-ICP-MS for elemental speciation of positive, neutral and negative species are discussed. Issues in interfacing CE and ICP-MS are considered briefly. The potential advantages and disadvantages of laminar flow in CE-ICP-MS are examined. Potential difficulties in CE-ICP-MS including loss of sample, chemical matrix effects and changes in speciation during separation are discussed. The interpretation of ES or IS-MS spectra and analysis of complex mixtures are considered. Calibration and chemical matrix effects are assessed. Potential pitfalls of interpreting bare metal ion spectra as elemental analysis are discussed. The need for fundamental understanding of the processes that control ES and IS-MS signals is examined. High conductivity samples currently present difficulties for CE-ICP-MS or ES and IS-MS.

Ionic Strength Dependence of Transition and Heavy Metal Adsorption onto Metal Oxides

Transition and heavy metal adsorption onto metal oxides influences the global cycling of metals, plays a role in the formation of enriched metal deposits, and filters natural and waste waters in the subsurface environment. The ionic strength dependence of metal adsorption is important to geochemists because natural waters are composed of different electrolyte types and vary widely in ionic strength. It is generally accepted that transition and heavy metal adsorption onto metal oxides does not exhibit an ionic strength dependence and that this behaviour indicates that metals bind to solid surfaces as inner-sphere complexes. However, Fig. 1 illustrates that while Cd adsorption from NaNO3 solutions onto goethite (Hayes and Leckie, 1987) does not exhibit major variations with ionic strength, Cd adsorption from NaCI solutions onto y-alumina (Kosmulski, 1996) progressively decreases with increasing ionic strength, and Cd adsorption from NaCIO4 solutions onto 7-alumina (Kosmulski, 1996) may increase with increasing ionic strength. An analysis of these datasets and many others reported in the literature indicates that transition and heavy metal adsorption is very strongly dependent on the nature of the electrolyte, and may increase, decrease, or exhibit little variation with increases in the ionic strength of the solution. In this study, experimental data for the adsorption of numerous transition and heavy metals onto quartz, silica, alumina, corundum, goethite, anatase, magnetite and manganese dioxide, from NaC104, NaNO3, KNO3, and NaC1 solutions, over a wide range of ionic strengths, have been fit using the triple layer model of Sahai and Sverjensky (1997), and at most two metal surface complexes. This model accounts for the ionic strength dependence of aqueous ion activity coefficients through the use of the extended Debye-Huckel expression. It is accompanied by a database of surface site densities, capacitances, and equilibrium constants for surface protonation, deprotonation, and electrolyte adsorption, which was modified to accommodate reported surface titration data and experimentally-determined points of zero charge. Recent applications of the triple layer model have suggested that divalent transition and heavy metals (M 2+) form simple surface species such as >SOM + in nitrate solutions (Hayes and Leckie, 1987; Katz and Hayes, 1995). However, using the triple-layer model of Sahai and Sverjensky (1997), surface complexes of the form >SOHM2+_NO3, where M 2+ is bound to a neutral surface site (>SOH) on the 0-plane of the triple layer model and NO3 is on the ]3-plane, are found to best fit data collected over a wide range of ionic strengths for Cd and Pb adsorption onto goethite (Hayes and Leckie, 1987) and Co adsorption onto corundum (Katz and Hayes, 1995). A similar type of surface complex >SOM+_NO3 fits the adsorption data for UO2 onto hydrous ferric oxide at pH values where the system can be assumed to be depleted in CO2. A combination of two complexes, including >SOHM2+_NO3 was found to fit Zn adsorption onto anatase (James and MacNaughton, 1977). In addition to sharing a common electrolyte, the systems described above have several other common characteristics: (a) the solids have intermediate-range dielectric constants between 10 and 22, (2) metal adsorption occurs on positively-charged surfaces, and (3) MNOfis the predominant aqueous complex over the pH range of adsorption and the range of ionic strengths studied. The one exception to (3) is Zn adsorption onto anatase, which required a second surface complex, >SOZnOH, to fit the adsorption data at low ionic strengths, where ZnOH-is the predominant aqueous complex. Adsorption of the predominant aqueous complex rather than the more abundant bare metal ion may be favoured because the free energy of solvation is smaller for a monovalent cationic complex (e.g. MNO3 + or MOH § than for a divalent cation (i.e. M 2+) (James and Healy, 1972). Metal-ligand complexation is also favoured in low dielectric constant environments like the interface. Metal adsorption data over a wide range of ionic strengths in NaC1 and NaC104 solutions are more limited. Calculations for Cd adsorption from NaC1 and NaC104 solutions onto 7-alumina are best matched by calculations using the surface complexes,

Electrospray Mass Spectrometry as a Technique for the Elemental Analysis of Metals and Organometals

An investigation of an in-house constructed electrospray (ES) ion source and interface has been carried out with the focus on elemental analysis. An evaluation of the 29, 30 and 31 gauge capillary sizes for the ES source is presented. For multi-element solutions of alkali metals, alkaline earth metals and transition metals studied in the bare metal ion mode, the smaller 30 gauge capillary improved the detection limits by an order of magnitude over those of the larger 29 gauge. The 31 gauge was too fragile for easy handling. The ion-cluster modes of Cr II , Cr III and Co II were investigated and the resulting spectra indicate the possibility of attaining speciation information with this set-up. Matrix effects on the analyte signal of a multielement solution of transition metals using the 29 and 30 gauge capillaries are discussed. The same trend is observed with both capillaries where the signal intensity improves with the addition of 0.15% and 0.30% total dissolved solids. At higher concentrations of total dissolved solids signal suppression is seen. Additionally, ES-MS was demonstrated as an elemental analysis tool for the study of the bare metal ion mode of larger organometallics, mainly organolead compounds and metalloporphyrins.