Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2006. / "Title from dissertation home page (viewed June 28, 2007)." Source: Dissertation Abstracts International, Volume: 67-06, Section: B, page: 3109. Adviser: Gary M. Hieftje.

The work presented is a systematic investigation of silica-based sorbents using solid-phase extraction (SPE). Properties of various cation exchangers and mixed beds comprised of strong cation exchange particles and alkyl-modified silica particles were explored. The role of ionic and nonpolar interactions was examined in terms of retention and elution of analytes. A series of displacement experiments was used to characterize the interactions and energy-minimized, three-dimensional models were used to illustrate these interactions. Selectivity of cation exchangers was probed by introducing cations differing in size, hydrophobic nature and charge before and after introduction of the analytes. The ionic strength, the solvent composition and the pH of the liquid phase were parameters that were varied in order to define the type of interaction that was responsible for retention, lack of retention, or elution during the SPE procedure. Application of mixed sorbents toward the extraction of basic drugs of abuse, as well as the use of reversed-phase silica and a resin for the extraction of a neutral organonitrogen species were also investigated. With propylene-linked cation exchangers (under appropriate pH conditions), it was shown that the primary mode of interaction is through ionic forces. As a consequence, there is no selectivity of these sorbents for cations based on hydrophobic nature. With ethylbenzene and octylene-linked exchangers, there is an increase in selectivity for cations with increasing hydrophobic nature. The linker chain is adequately long enough to allow for nonpolar interactions with the aliphatic side groups, just as a resin-based exchanger allows. With short and long chain exchangers, there is selectivity proportional to the charge of the ion. The proposed reason for this is a combination of multiplesite attachment of polyprotic species to the surface and increased probability of single-site interaction proportional to the number of charged nitrogen atoms on the molecule. It was shown that mixed sorbent beds offer advantages in operator control over the retention of organic bases in a high ionic strength sample matrix. The retention mechanism was elucidated, demonstrating a clear contribution of nonpolar forces to retention with the mixed sorbents as was observed with the long-chain cation exchangers.

The modified surface of solid phase extraction sorbents is studied with respect to the impact on the isolation and purification of analytes. Interactions at the interface are characterized by quantifying recoveries of a broad range of analytes, on a variety of surfaces, and under various extraction conditions. Bonded phases of varying hydrocarbon chain length are studied. A hydrophobic surface (e.g., C18) favors the retention of small polar compounds, while a more polar surface (C2) favors the elution of larger hydrophobic compounds. A compromise phase (C8) improves overall recoveries, while analyte recoveries were optimized by extraction onto stacked and layered phases. Analytes are retained by different mechanisms and under different solvent conditions. Selective elution of analytes is achieved by judiciously choosing the elution solvent. Data obtained from comparing the time requirements for drying various phases are consistent with previously developed models of the bonded silica surface. The impact of the presence of water on the elution of analytes is also studied. Experiments are presented where increasing concentrations of organic solvent are added to the sample matrix. Recoveries for polar compounds dropped as the matrix became more energetically favorable. Recoveries improved for hydrophobic species as the formation of agglomerations was disrupted. The impact of sample loading rates on analyte recoveries is studied. No significant differences in recoveries of a broad range of non-ionizable analytes are observed for loading rates ranging from 8 to 30 mL per minute on a 13 mm diameter x 15 mm height sorbent bed. The impact of the porous nature of the extraction sorbent on analyte recoveries, under different conditions of temperature and solvent contact time, is studied. A dependence on the diffusion of analytes into and out of the pores is observed. Experiments are devised to characterize the role of particulates in the sample matrix during solid phase extraction. Parameters studied include size of particles in the matrix, in the sorbent bed, porosity of the frit retaining the sorbent, and utility of a depth filter. Samples laden with particulates are spiked with trace analytes and show no reduction in recoveries resulting from the presence of particulate matter.

This document describes the development of spectroscopic techniques which benefit from the use of charge-transfer devices. Both charge-coupled devices (CCD's) and charge-injection devices (CID's) are used in the techniques presented here such as atomic emission spectroscopy and latent fingerprint imaging. The use of a CID echelle system for axial viewing of the inductively coupled plasma (ICP) demonstrates the enhancement in sensitivity that can be obtained over tangential viewing. More importantly though, are the advantages afforded by simultaneous multi-element detection. Axial viewing of the ICP has shown to not only improve upon the detection limits of several metals by, in some cases, a half order of magnitude, but also to increase the amount of light collected and thus reduce the time of analysis. Along with this, the effect of interferences upon the detection of various metals is, at worst, equivalent to that of an ICP with tangential viewing. Further enhancement of sensitivity in atomic analysis can be achieved by atomic fluorescence with an ICP. Although in the past, hollow cathode lamps have proven to be insufficient, advanced designs of hollow cathode lamps presented here have demonstrated an increase in the intensity of lines of copper best suited for use in ICP atomic fluorescence. Lastly, a latent fingerprint has been imaged with the use of a scientific CCD and a flashlight where in the past such a technique was accomplished with high power lasers. By using a CCD, the immediate digitization of information combined with the sensitivity and image processing capabilities offer a portable means by which to image latent fingerprints on poor surfaces.

No description available.

$\sp{23}$Na and $\sp7$Li NMR have proven to be very useful techniques for studying the extent of complexation reaction of lithium and sodium cations with 15-crown-5 (15C5) and benzo-15-crown-5 (B15C5) in nitromethane (NM), acetonitrile (AN), pyridine (PY) and dimethylformamide (DMF). Although the formation constants (K$\sb{\rm F1})$ of (Na:15C5)$\sp+,$ (Na:B15C5)$\sp+,$ (Li:15C5)$\sp+$ and (Li:B15C5)$\sp+$ in NM were too large to be accurately measured (log K$\sb{\rm F1}$ $>$ 4), that of (Na:B15C5)$\sp+$ in DMF and PY were determined from $\sp{23}$Na chemical shift and longitudinal relaxation rates: log K$\sb{\rm F1}$ = 2.9 $\pm$ 0.3 in PY and 1.2 $\pm$ 0.4 in DMF. A combined $\sp{23}$Na and $\sp7$Li NMR study for systems containing both lithium and sodium cations in the presence of B15C5 in NM revealed a selectivity for the complexation of lithium where the equilibrium constant, reflecting the ratio K$\sb{\rm FLi}$/K$\sb{\rm FNa},$ was determined: log K$\sb{\rm eq}$ = 1.9 $\pm$ 0.2. In the two-site chemical exchange of the alkali metal cations, two exchange mechanisms have accounted for the $\sp{23}$Na and $\sp7$Li dynamic NMR results: associative and dissociative exchange. The chemical exchange of sodium and lithium individually with B15C5, was shown, by $\sp{23}$Na and $\sp7$Li NMR respectively, to follow the associative pathway in NM whereas in AN the chemical exchange of sodium with B15C5 was shown to prefer the dissociative pathway. Kinetic studies of sodium-B15C5 in binary mixtures of AN-NM and DMF-NM have indicated that the change in observed mechanism is related to the solvent donicity where dissociative exchange is observed in high donicity solvents. An increase of the concentration of AN or DMF in the solvent mixture gives rise to an increase of the dissociative contribution to the exchange. The activation parameters of the dissociative exchange are highly solvent dependent indicating that the solvent, at the molecular level, must play an important role in this mechanism. However, the activation parameters for the associative exchange do not display such a dependence on the solvent; it was postulated that conformational rearrangements play the governing role in this mechanism. In studies with DMF-NM binary solvent mixtures, a model based on the direct participation of one DMF molecule in the coordination sphere of sodium in (Na:B15C5)$\sp+,$ has accounted for the observed $\sp{23}$Na chemical shift and longitudinal relaxation rate variations of (Na:B15C5)$\sp+$ as a function of the concentration of DMF in the solvent mixture. It was postulated that it is the formation of (Na:B15C5:DMF)$\sp+$ which is responsible for the observed increase of the rate of exchange as the concentration of DMF in the solvent increases. This direct participation of one solvent molecule in the dissociative exchange was qualitatively and quantitatively characterized. The application of 2-dimensional $\sp7$Li exchange NMR spectroscopy (EXSY), for the kinetic investigations of the exchange of the lithium cation in its solvated (NM) and complexed (B15C5) sites, is illustrated. Results obtained by this method are in agreement with the conventional 1D lineshape results. (Abstract shortened by UMI.)

No description available.

This thesis is directed towards the study of the solvent extraction behaviour of the lanthanides and aluminium, bismuth, calcium and zinc whose radii and/or charges are similar to those of the REE. A brief review of the fundamentals and classification of extraction systems and of extractants is presented in Chapter 1. Chapters 2 and 3 are reviews of the properties and uses of the lanthanides and solvent extraction using phosphonate and sulphonate extractants, respectively. Chapter 4 deals with experimental procedures, results, discussions and conclusions. The extraction of zinc (II), calcium (II), aluminium (III), bismuth (III) and some lanthanide ions from aqueous perchlorate solutions into hexane solutions of 2-ethylhexyl phenylphosphonic acid, HEH$\Phi$P, was studied. The mechanisms of extraction are discussed on the basis of the results obtained by slope analysis. Depending upon the size and charge of the ion, the extracted species contain varying numbers of extractant molecules and phosphonate groups as ligands. Monomeric complexes are formed in the presence of excess extractant. High loadings of the extractant phase with the metal ion resulted in suppression of the extraction. Alkali ions were not extracted but alkali perchlorate suppressed the extraction through the effect of ionic strength on the metal ion activity. To further investigate the mechanism of extraction, $\sp{31}$P NMR of the organic phase following extraction of lanthanum was studied. A polymeric lanthanum-HEH$\Phi$P complex which precipitates out in the organic phase is formed at high (saturation) loading of this phase. A structure is proposed for this complex. The thermodynamics of extraction of these ions from perchlorate solutions into petroleum ether solutions of dinonylnaphthalene sulphonic acid, DNNSA, and HEH$\Phi$P were studied. In the case of DNNSA, extraction of the trivalent ions is dominated by the enthalpy of complexing. Electrostriction of large complex micelles by the complexed ion is postulated in order to account for the entropy effect. For the divalent ions, the enthalpy of dehydration of the ion is more important. A strategy for improving the separation factors is proposed. In the case of HEH$\Phi$P, charge density of the cation has a major influence upon the mechanism of the reaction and in turn upon the thermodynamic parameters. The ionic strength of the aqueous phase influences the thermodynamic parameters in the HEH$\Phi$P and DNNSA systems. Amongst the REE, lanthanum shows a singular behaviour. The extractions have been compared with those that employ dinonylnaphthalene sulphonic acid and factors that are responsible for the greater selectivity of the phosphonate have been elucidated. Development of an extraction chromatographic separation procedure for the lanthanides with a view to separating them from other matrix elements and fractionating them among themselves was studied. This was to be achieved by employing an organic polar solvent in the later stages of column elution. However, low recoveries were observed upon ashing the organic eluent and DCP determinations. The presence of phosphate (as KH$\sb2$PO$\sb4$ or H$\sb3$PO$\sb4)$ was found to lead to depression of analyte signal (concentration) in the DCP.

In this thesis, the investigation of the mechanism of chlorine evolution reaction at (i) both freshly reduced and pre-oxidized Pt electrodes; (ii) RuO$\sb2$-TiO$\sb2$ electrodes (DSA); (iii) other noble metals such as Pd, Ir, Ru and Rh by means of computer controlled anodic polarization, potential-relaxation transients and a.c. impedance measurements, will be presented. As described in Chapter V, the influence of co-deposited OH and O species in the surface oxidation process on the extent of chemisorption of the Cl$\sp-$ intermediate in the Cl$\sb2$ evolution reaction has been carefully examined. Experimental results reveal that the reaction rate at reduced Pt surfaces is much greater than that at pre-oxidized ones. This is because the oxide species have a significant effect in blocking the Cl$\sb2$ evolution kinetics. The detectable surface adsorption pseudocapacitance, which is associated with the "overpotential deposited" Cl$\sp-$ intermediate, at freshly reduced Pt and oxide free Pt surfaces in non-aqueous trifluoroacetic acid (TFA) medium supports this conclusion. In Chapter VI, some exploratory experiments at other noble metal (e.g., Pd, Ir, Ru, and Rh) electrodes in non-aqueous TFA solution have shown very interesting interfacial capacitance information, which must be interpreted probably in terms of more than one adsorbed reaction intermediate being present. In Chapter VII, a possible mechanism of recombination kinetically control has been proposed for the Cl$\sb2$ evolution reaction at RuO$\sb2$-TiO$\sb2$ electrodes, based on the observations of their steady-state behaviour, and electrochemical data from potential relaxation and a.c. impedance measurements. Local supersaturation of Cl$\sb2$ in the microstructure of the oxide film appears to make a contribution to the pseudocapacitance behaviour. Some of the results in this work have been published or in press, as listed below: (1) "Surface electrochemistry of the anodic chlorine evolution reaction at Pt influence of co-deposition of the Cl$\sp-$ intermediate", P. Gu and B. E. Conway, J. Chem. Soc. Farada Trans. 86(6) (1990) 923. (2) "Behaviour of the adsorbed Cl$\sp-$ intermediate in anodic chlorine evolution at thin-film RuO$\sb2$ surfaces", P. Gu and B. E. Conway, J. Appl. Electrochem., in press. (3) "Evaluation of Cl$\sp-$ adsorption in anodic chlorine evolution at Pt by means of a.c. impedance and potential relaxation experiments: role of the state of surface oxidation", P. Gu and B. E. Conway, J. Chem. Soc. Faraday Trans., in press.

The work presented in this thesis is primarily focused on the development of pre-fluorescent probes for carbon-centered radicals. Coumarin-TEMPO and quinoline-TEMPO adducts have been prepared by tethering a free radical nitroxide group such as 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to coumarin and quinoline fluorophores through an ester bond. Some organic derivatives of the quinoline-TEMPO adduct are also presented. Intramolecular quenching of fluorescence due to a spin-exchange mechanism between the singlet excited state of the fluorophore and the doublet ground state of the nitroxide and the restoring of fluorescence due to coupling with a carbon-centered radical are the conceptual bases for this research study. (Abstract shortened by UMI.)