1. A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide*.
- Author
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Thornton, Brett F., Horst, Axel, Carrizo, Daniel, Holmstrand, Henry, Andersson, Per, Crill, Patrick M., and Gustafsson, Örjan
- Subjects
HALOGENS ,CHROMATOGRAPHIC analysis ,BROMOMETHANE ,NUCLEAR spectroscopy ,GAS chromatography - Abstract
A system was developed for collecting from the ambient atmosphere the methyl halides CH
3 Cl and CH3 Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3 Cl and CH3 Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3 Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min−1 is applied to yield the nearly 40 ng required for subsequent δ81 Br-CH3 Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Δ81 Br isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3 Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Δ81 Br-CH3 Br of +0.03‰ ± 0.10‰ relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever δ81 Br-CH3 Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding −0.08‰ ± 0.43‰ and +1.75‰ ± 0.13‰ versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site. [ABSTRACT FROM AUTHOR]- Published
- 2013
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