Protocols for the quantification of dimethyl sulfide (DMS) and other volatile organic compounds in aquatic environments

Aquatic environments produce a range of volatile organic compounds (VOCs) that can transfer into the atmosphere and affect climate. Much of our understanding on the biogeochemistry of volatiles in seawater stems from research on the biogenic trace gas dimethyl sulfide (DMS). Here, we describe four protocols for the quantification of DMS and other VOCs in aqueous samples that utilise direct injection or cryogenic enrichment techniques before separation and quantification using gas chromatography with flame photometric detection (GC-FPD). With few adjustments, the protocols can be customised to quantify a range of other gases including hydrocarbons such as isoprene and ethene, or halocarbons such as methyl chloride or bromoform. The limit of quantification for DMS is 1.5 pmol and the protocols range in sensitivities for DMS from 0.2 to 20 μM (direct injection of 200 μL headspace), 50 to 250 nM (headspace purging of 1.92 mL gaseous phase), 0.5 to 350 nM (in-vial purging of 3 mL aqueous phase), and the sub-nanomolar range for in-tube purging of sample volumes up to 200 mL. Two additional adaptations of the protocol include quantification of the biological DMS-precursor dimethylsulfoniopropionate (DMSP) and the DMS-oxidation product dimethyl sulfoxide (DMSO).