Articles | Volume 11, issue 2
Ocean Sci., 11, 313–321, 2015
https://doi.org/10.5194/os-11-313-2015
Ocean Sci., 11, 313–321, 2015
https://doi.org/10.5194/os-11-313-2015

Technical note 23 Apr 2015

Technical note | 23 Apr 2015

Technical Note: A fully automated purge and trap GC-MS system for quantification of volatile organic compound (VOC) fluxes between the ocean and atmosphere

S. J. Andrews, S. C. Hackenberg, and L. J. Carpenter S. J. Andrews et al.
  • Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, The University of York, York, YO105DD, UK

Abstract. 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 (CH22l, kHcc 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 CH22l within the surface ocean water.

Download
Short 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. Here we describe a gas chromatograph mass spectrometer based purge and trap system that was developed for the fully automated analysis of dissolved very short-lived species (VSLS) in seawater sampled from a research ship.