A simple headspace equilibration method for measuring dissolved methane

Limnology and Oceanography: Methods
By: , and 

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Abstract

Dissolved methane concentrations in the ocean are close to equilibrium with the atmosphere. Because methane is only sparingly soluble in seawater, measuring it without contamination is challenging for samples collected and processed in the presence of air. Several methods for analyzing dissolved methane are described in the literature, yet none has conducted a thorough assessment of the method yield, contamination issues during collection, transport and storage, and the effect of temperature changes and preservative. Previous extraction methods transfer methane from water to gas by either a "sparge and trap" or a "headspace equilibration" technique. The gas is then analyzed for methane by gas chromatography. Here, we revisit the headspace equilibration technique and describe a simple, inexpensive, and reliable method to measure methane in fresh and seawater, regardless of concentration. Within the range of concentrations typically found in surface seawaters (2-1000 nmol L-1), the yield of the method nears 100% of what is expected from solubility calculation following the addition of known amount of methane. In addition to being sensitive (detection limit of 0.1 ppmv, or 0.74 nmol L-1), this method requires less than 10 min per sample, and does not use highly toxic chemicals. It can be conducted with minimum materials and does not require the use of a gas chromatograph at the collection site. It can therefore be used in various remote working environments and conditions.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A simple headspace equilibration method for measuring dissolved methane
Series title Limnology and Oceanography: Methods
DOI 10.4319/lom.2014.12.637
Volume 12
Year Published 2014
Language English
Publisher American Society of Limnology and Oceanography
Publisher location Waco, TX
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description 14 p.
First page 637
Last page 650
Online Only (Y/N) N
Additional Online Files (Y/N) N