| A novel analytical method using Needle Trap (NT) devices and a gas chromatograph mass spectrometer (GC-MS) system to quantify marine volatile organic compounds (VOC) relevant to atmospheric chemistry has been developed and applied for the first time on sea-water samples. Purging gases from small water volumes (10ml) onto sealable needles followed by thermal desorption directly in the GC injector provided efficient analysis of a wide range of VOCs (DMS to a-pinene) within 20 minutes. The novel aspect in this method is that water vapor collected within the NT during sampling is used to drive the collected VOC from the adsorbent. Good repeatability, linearity and limits of detection as low as few ngr/L were obtained for all the examined compounds. Following laboratory validation the NT - method was applied in a mesocosm field study in a Norwegian Fjord. Nine individual mesocosm ecosystems under different CO2 regimes were examined. Dimethylsulphide (DMS), isoprene and monoterpenes were identified in mesocosm seawater and their response to increasing ocean acidity was studied during a bloom evolution (26 days). The DMS measurements are compared with parallel measurements provided by an independent GC-FID system. The average of nine mesocosms showed a correlation of R2=0.75 between the two techniques. Our study indicates that the NT-method can be used successfully in place of the traditionally used techniques for DMS analysis in sea-water while extending the range of VOC to C10 species. |
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