This paper has been accepted for publication in Analytical Chemistry. DOI: 10.1021/acs.analchem.5b03102 Please contact Cara Manning (
[email protected]) for the typeset version of the paper.
Supporting information for: Continuous Measurements of Dissolved Ne, Ar, Kr, and Xe Ratios with a Field-deployable Gas Equilibration Mass Spectrometer Cara C. Manning,∗,†,‡ Rachel H. R. Stanley,¶,‡ and Dempsey E. Lott III‡ Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography, Woods Hole, MA, Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, and Department of Chemistry, Wellesley College, Wellesley, MA E-mail:
[email protected]
Introduction In the Supporting Information, we present ancillary information that will be useful to researchers who plan to build a gas equilibration mass spectrometer (GEMS) and/or modify the method described in the main paper. We describe alternate configurations that were tested, and the instrument settings used for the mass spectrometer. We provide photos of the GEMS (Figures S5–S7), a schematic of the custom-made getter chambers (Figure S1), and tables of the parts used (Tables S3 and S4). We show the field data collected in Waquoit Bay before and after calibration with discrete samples, along with the calibration curves used. Additionally, we discuss the effect of vibrations on the data quality. ∗ To
whom correspondence should be addressed Joint Program ‡ Woods Hole Oceanographic Institution ¶ Wellesley College † MIT/WHOI
S1
Alternative configurations tested Water flow configuration: On a research vessel, we tested a setup where the underway seawater stream flowed directly from the filter canisters into the membrane contactor (avoiding the need for overflowing water, thereby simplifying the setup). However, we found that the gas mole ratios measured were inaccurate in this configuration, based on comparison of the GEMS data with discrete samples. We hypothesize that back pressure within the underway line may have altered the equilibration kinetics within the membrane contactor. By pumping the water into a bucket, which is open to the ambient air, and then sampling from the bucket, we allow the water to depressurize before it enters the membrane contactor. We minimize gas exchange within the bucket by using a high water flow rate, so that the residence time of water in the bucket is
