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On Flasks

COS concentrations are apparently stable for months in electro-polished stainless steel flasks.  Ambient air collected by the South Pole, where humidity was very low, showed differences between glass flasks and electro-polished stainless steel flasks, whereas air collected at a more humid site did not show large differences in flask type (Montzka et al., 2004).
For silica-coated flasks (e.g. from Restek, Bellafonte, PA, USA), the age of the silica coating can affect the stability of reduced sulfur compounds (Khan et al., 2012).

Currently,
  • the best flask for high pressure gas storage is an Essex steel flask.
  • the best flask for low pressure (<40 psi) gas storage is a Restek silcosteel flask.

When sampling with programmable flask packages or other samples that require a compressor pump, it is essential to replace rubber O-ring parts and diaphragms with more inert material.  A rubber diaphragm pump can introduce several parts-per-billion COS into the sample stream.  The "version 3" PFP and PCPs are usually okay for OCS sampling, but each individual piece of equipment should be checked (e.g. fill the PFPs with nitrogen through the compressor then check for zero OCS) before field deployment.  
This material is based upon work supported by the National Science Foundation under Grant Number 1433257.  
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. 
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