UVM Theses and Dissertations
Format:
Print
Author:
Small, Colleen
Title:
Dept./Program:
Chemistry
Degree:
MS
Abstract:
The analysis of cosmogenic ²⁶Al is important in any areas of the Earth, climate, and space sciences owing to its long half-life (7.20 ka) and its mode of production in the atmosphere. Accelerator mass spectrometry (AMS) is the only method known that is sensitive enough to measure the trace concentrations of c smogenic nuclides found in natural samples. However, the analysis of cosmogenic²⁶Al is a challenge for many AMS facilities because it does not generate high ion beam currents to give precise measurements. Cosmogenic²⁶Al is generally analyzed in the chemical form of Al₂O₃; however, it was recently found in this laboratory that metallic aluminum generates higher ion beam currents than Al₂O₃. The goal of this research was to improve the ion beam current of cosmogenic ²⁶Al by AMS by the evaluation of several methods for enhancing ion production rates for ²⁶Al through manipulation of its chemical form; namely by (1) the electrochemical reduction of Al³ by employing a chelating agent and (2) applying the chelating agent to preconcentrate the Al³ and measuring it by AMS.
Two different widely studied chelating agents were chosen, oxine and altol, to carry out the electrochemical reduction. The cathodic electrochemical ehavior of aluminum-oxine complexes has been well documented and been used to quantify aluminum in water samples. In this study, we altered the experiment presented in literature by employing a solid electrode instead of a hanging mercury drop electrode. We were unable to reduce the Al³, and discovered that the oxine is reduced first when employing a solid electrode. This led us to choose maltol, a chelating reagent that is more difficult to reduce than Al³. To our knowledge, this is the first study of the electrochemical reduction behavior of the aluminium-maltol complex. Our voltammetric experiments of the aluminum-maltol complex revealed an irreversible process with two reductions that occur simultaneously, with one reduced specie close to the reduction potential of maltol.
We determined the process was a 3-electron transfer by controlled potential electrolysis (CPE). The Al³ is not completely reduced because the reduction of maltol is a 2-electron transfer process. Due to the scope of our work, we did not proceed further with the study of the aluminum-maltol complex. Simultaneously, we pursued the use of oxine as a preconcentrating agent for Al³ for AMS analysis. The aluminum-oxine comple is a weaker compound compared to ceramic Al₂O₃ (i.e., ~300 °C .boiling point versus 2072 °C, respectively), and therefore the Alq₃ was hypothesized to produce Al⁻ ions more readily because its lattice forces are weaker. A method to reproducibly prepared Alq₃ was developed for two different mediums, water and pH 5 buffer. A set of Alq₃ samples was analyzed at the Center of Accelerator Mass Spectrometry (CAMS) in Livermore, CA under optimal parameters employed for ²⁶Al analysis using Al₂O₃ samples.
Unfortunately, some of the samples melted and ion current signals could not be stablized for any samples, preventing acquisition of reliable ion count data. This study suggested that the parameters used for Al₂O₃ could not be used for Alq₃. A second set of Alq₃ samples was analyzed at the Natural Environmental Research Center (NERC) in Scotland and different parameters were applied. In this case, the Alq₃ samples did not melt, however, higher ion beams were not obtained. Nonetheless, the complexation selectivity of oxine for Al³ over Mg² may permit the use of the AlO⁻ion, which yields higher beam currents than, while mitigating interference from ²⁶Mg. This was the first time that Alq₃ was analyzed by AMS.
Two different widely studied chelating agents were chosen, oxine and altol, to carry out the electrochemical reduction. The cathodic electrochemical ehavior of aluminum-oxine complexes has been well documented and been used to quantify aluminum in water samples. In this study, we altered the experiment presented in literature by employing a solid electrode instead of a hanging mercury drop electrode. We were unable to reduce the Al³, and discovered that the oxine is reduced first when employing a solid electrode. This led us to choose maltol, a chelating reagent that is more difficult to reduce than Al³. To our knowledge, this is the first study of the electrochemical reduction behavior of the aluminium-maltol complex. Our voltammetric experiments of the aluminum-maltol complex revealed an irreversible process with two reductions that occur simultaneously, with one reduced specie close to the reduction potential of maltol.
We determined the process was a 3-electron transfer by controlled potential electrolysis (CPE). The Al³ is not completely reduced because the reduction of maltol is a 2-electron transfer process. Due to the scope of our work, we did not proceed further with the study of the aluminum-maltol complex. Simultaneously, we pursued the use of oxine as a preconcentrating agent for Al³ for AMS analysis. The aluminum-oxine comple is a weaker compound compared to ceramic Al₂O₃ (i.e., ~300 °C .boiling point versus 2072 °C, respectively), and therefore the Alq₃ was hypothesized to produce Al⁻ ions more readily because its lattice forces are weaker. A method to reproducibly prepared Alq₃ was developed for two different mediums, water and pH 5 buffer. A set of Alq₃ samples was analyzed at the Center of Accelerator Mass Spectrometry (CAMS) in Livermore, CA under optimal parameters employed for ²⁶Al analysis using Al₂O₃ samples.
Unfortunately, some of the samples melted and ion current signals could not be stablized for any samples, preventing acquisition of reliable ion count data. This study suggested that the parameters used for Al₂O₃ could not be used for Alq₃. A second set of Alq₃ samples was analyzed at the Natural Environmental Research Center (NERC) in Scotland and different parameters were applied. In this case, the Alq₃ samples did not melt, however, higher ion beams were not obtained. Nonetheless, the complexation selectivity of oxine for Al³ over Mg² may permit the use of the AlO⁻ion, which yields higher beam currents than, while mitigating interference from ²⁶Mg. This was the first time that Alq₃ was analyzed by AMS.