This project involves an evaluation of the use of electrochemical techniques to improve the efficiency of metal ion production of liquid glass ion emitters. Overall, the project is designed to allow thermal ionization mass spectrometry (TIMS) to generate higher precision elemental isotope ratio measurements than is currently possible for elements of geologic interest (such as Pb). In this project we will investigate the use of modern electrochemical techniques to increase the efficiency of molten glass ion emitters (aka "Si gel" ion emitters). Recent studies from the analytical chemistry community have provided new insights into the processes of ion emission from liquid glasses. These studies have suggested that under the operating conditions in mass spectrometer, metal dopants in borosilicate glass melts (including Pb and Ag) are dominantly present as neutral metal atoms. This opens the possibility that increasing the proportion of metal ions in the glass could result in a more intense emitted metal ion beam. Our work will involve exploring the electrochemical properties of molten glasses under high vacuum, the conditions experienced in the source of a thermal ionization mass spectrometer. We will use a vacuum chamber "test bench" retrofitted for electrochemical experiments and square wave voltammetry to assess the oxidation-reduction behavior of metals (Pb, Mo, Fe, Cu, etc.) doped in molten borosilicate glasses. The experimental apparatus has already by constructed and simple cyclic voltammagrams of molten borosilicate glasses have already been generated, demonstrating the feasibility of our approach. Our experiments will be used to determine the optimal electrode potentials required to produce sustained anodic currents in the molten glasses, the anodic currents corresponding to oxidation of the metal dopants. Armed with this information we will design and construct an electrochemical cell that can be used in our existing Finnigan-MAT 261 TIMS and determine if the anodic currents generated in the molten glasses result in increased ion emission from these glasses for various metal dopants. If successful, this project should lead to higher precision age determinations for geologic materials, using U-Pb techniques, and will have implications to other disciplines requiring high precision elemental isotopic ratio determinations, including biochemistry and nuclear forensics. Most of the work will be carried out as part of the dissertation research of a female, Hispanic PhD student in the Department of Geological Sciences, University of Colorado, Boulder.
High precision measurements of the isotopic compositions of various elements in Earth are a key to improving our ability to determine the age and mechanisms of many Earth processes. This project involved developing a new technique for producing "thermalized" ions for use in thermal ionization mass spectrometers. The idea is to generate a larger fraction of "ions" from a sample of an element for which higher precision isotope data is required. Increasing the ionization efficiency of ion sources means more ions are generated and measured in the mass spectrometer, and increases the precision of the isotopic abundance measurements made. Our approach is to apply electrochemical techniques to increase the number of ions emitted from molten silicate liquid that has been "doped" with a sample of a given element, such a lead. We developed methods of conducting eletrochemical experiments in situ at high temperature and under vacuum conditions and demonstrated that for one element of great interest in geochronology, Pb, we can in fact induce oxidation/reduction reactions involving this element when it is doped in silicate melts . We also constructed a prototype "intedigitated electrode array" using semiconductor construction techniques, and this array represent the test bed we are using for ongoing experiments to create a high efficiency source of ions from molten glass.
