HR: 0800h
AN: V41D-1481    [Abstracts]
TI: An Electrochemical Approach to Improving the TIMS Ion Source
AU: * Cheversia, M B
EM: cheversi@colorado.edu
AF: Univ. of Colorado, Dept. of Geol. Sci., 2200 Colorado Ave., Boulder, CO 80309 United States
AU: Farmer, G
EM: farmer@colorado.edu
AF: Univ. of Colorado, Dept. of Geol. Sci., 2200 Colorado Ave., Boulder, CO 80309 United States
AB: Thermal ionization mass spectrometry (TIMS) is the method of choice for high precision isotope ratio measurements. However, demands for smaller sample sizes in geochronology and isotope tracer studies are challenging current capabilities of TIMS instrumentation. We have focused our efforts on improving the thermalized ion source in order to increase ionization efficiencies of typically analyzed elements, such as Pb. The current state of the thermalized ion emitter is a boro- or phosho- silica gel doped with the element of interest and loaded onto a resistively heated Re or Ta filament. To date, little is known about the ion formation mechanism in the silica gel, and typical ionization efficiencies for elements such as Pb, Cr, Ru, and Ag are in the range of 0.05-2%. Previous workers found that Ag-doped borosilicate glasses heated under high vacuum emitted monatomic metallic species, predominately Ag⁰ with subordinate Ag⁺. As suspected, under low fO₂ conditions, elements exist in their reduced state. We have attempted to use modern electrochemical methods to increase the abundance of oxidized metal ions emitted from the molten borosilicate glass ion emitter. By treating the molten glass as the electrolyte in the electrochemical cell, and varying the voltage to Pt reference and counter electrodes, we aim to find the potential range to oxidize the doped metal element from neutral to ionized species, and therefore increase the number of analyzable ions within the mass spectrometer, and hence directly increase the ionization efficiencies and analytical precision of measured isotope ratios. We have built a high vacuum test chamber in which to perform electrochemical experiments. Thus far, we have produced a simple cyclic voltammogram that shows that even with the borosilicate glass heated to 1600°C, the glass is acting as a resistor, and is not completely molten, which is essential to mimic mass spectrometer conditions, and to using the glass as the electrolyte in the electrochemical cell. We will continue to perform experiments in order to determine the potential in which to oxidize a doped metal element. Provided we achieve positive results with the test chamber, we will miniaturize our electrochemical cell so that it may function as the ion source within the sample chamber of the mass spectrometer.
DE: 1040 Radiogenic isotope geochemistry
DE: 1094 Instruments and techniques
DE: 1194 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005