Technical Note: A fully automated purge and trap GC-MS system for quantification of volatile organic compound (VOC) fluxes between the ocean and atmosphere
The oceans are a key source of a number of atmospherically important volatile gases. The accurate and robust determination of trace gases in seawater is a significant analytical challenge, requiring reproducible and ideally automated sample handling, a high efficiency of seaw...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-04-01
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| Series: | Ocean Science |
| Online Access: | http://www.ocean-sci.net/11/313/2015/os-11-313-2015.pdf |
| Summary: | The oceans are a key source of a number of atmospherically important
volatile gases. The accurate and robust determination of trace gases
in seawater is a significant analytical challenge, requiring
reproducible and ideally automated sample handling, a high efficiency
of seawater–air transfer, removal of water vapour from the sample
stream, and high sensitivity and selectivity of the analysis. Here we
describe a system that was developed for the fully automated analysis
of dissolved very short-lived halogenated species (VSLS) sampled from
an under-way seawater supply. The system can also be used for
semi-automated batch sampling from Niskin bottles filled during CTD
(conductivity, temperature, depth) profiles. The essential components
comprise a bespoke, automated purge and trap (AutoP & T) unit
coupled to a commercial thermal desorption and gas chromatograph mass
spectrometer (TD-GC-MS). The AutoP & T system has completed five
research cruises, from the tropics to the poles, and collected over
2500 oceanic samples to date. It is able to quantify >25 species over
a boiling point range of 34–180 °C with Henry's law
coefficients of 0.018 and greater (CH<sub>2</sub></sub>2l</sub>, <i>k</i><sub>H</sub><sup>cc</sup>
dimensionless gas/aqueous) and has been used to measure organic
sulfurs, hydrocarbons, halocarbons and terpenes. In the eastern tropical
Pacific, the high sensitivity and sampling frequency provided new
information regarding the distribution of VSLS, including novel
measurements of a photolytically driven diurnal cycle of
CH<sub>2</sub></sub>2l</sub> within the surface ocean water. |
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| ISSN: | 1812-0784 1812-0792 |