Date

2017

Department or Program

Chemistry

Primary Wellesley Thesis Advisor

Rachel Stanley

Abstract

The five stable noble gases (He, Ne, Ar, Kr, Xe) are useful tracers of physical processes in the environment, as they are biologically and chemically inert and respond solely to physical forcing. Most instrumental systems used for measurements of the suite of noble gases are expensive, low-throughput, and require laboratory support. Here we describe the development and optimization of a low-cost, high-throughput quadrupole mass spectrometer system for the measurement of noble gas ratios in water samples. This system is based around a Hiden 201 RC residual gas analyzer, which is coupled with a Bay Instruments membrane inlet for continuous gas extraction. This work is the first of its kind to use this particular membrane for measurements of noble gases; previously, these types of membranes have only been used in the study of other, more abundant gases. We evaluate the precision and accuracy of noble gas ratios as measured with this method. Our analysis of precision indicates that this instrument could be capable of measuring environmental samples if the most precise measurements could be consistently repeated. Preliminary data from accuracy experiments, however, suggests there is room for improvement before such a setup can be used in the field. Nevertheless, there are only a few other compact membrane-inlet QMS systems in development around the world, and our setup is already capable of measuring ratios more precisely and accurately than many of these analogous systems.

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