Determination of light hydrocarbons dissolved in seawater

A practical method for the on board determination of light (C1–C4) hydrocarbons dissolved in seawater has been developed. The gaseous hydrocarbons in seawater were extracted quickly with a vacuum sparge tower and determined gas chromatographically. By using two cryogenic columns at dry ice–ethanol temperature (−80°C) connected in series, it was possible to completely collect the hydrocarbons. The precision and sensitivity were comparable to that of previous methods. The analysis was completed within 45 min for one sample and the sample volume was 500 ml. The method was successfully applied to the northern North Pacific water collected in summer 1997. The concentrations of C2–C4 hydrocarbons in surface seawater ranged from several to several tens pmol l−1, within the range of concentrations in previous studies.