Determination of light hydrocarbon gases in sea water using three variants of static “equilibrium” headspace analysis

Abstract

Three methods for the determination of the light hydrocarbon gases methane, ethane, ethene, propane, propene, butane, 2-methylpropane and butenes in coastal sea water are described. The first two methods are based on manual equilibration of the headspace vapours in glass vessels, followed by injection into the gas chromatograph. The third method uses a commercial semi-automatic, pneumatically controlled headspace device interfaced to the gas chromatograph. Analysis is then performed using both packed and capillary column chromatography, followed by flame-ionisation detection. The limit of detection is below 2 × 10^–5 ml l^–1 v/v for method variant I and below 5 × 10^–6 ml l^–1 v/v for method variants II and III.