Methodology for analyzing dimethyl sulfide and dimethyl sulfoniopropionate in seawater using deuterated internal standards

A method is presented that provides good accuracy and precision for the determination of dimethyl sulfide (DMS) and its precursor dimethyl sulfoniopropionate (DMSP) in seawater for trials-based equipment. By using deuterated internal standards of DMS-d(6) and DMSP-d(6), the precision for replicate determinations was shown to be as high as 1.6% for DMS and 5.8% for DMSP when the internal standard concentration differed by up to 1 order of magnitude from the components being determined. The method for DMS using "commercial off the shelf" equipment gave a detection limit of 0.03 nM and was linear to > 100 nM. The DMSP method required slight modification to the equipment and gave a detection limit of 0.3 nM and was linear to > 1000 nM. The most appropriate sample preparation methodology for storing the samples for up to 56 h during intensive sampling periods included filtration, acidification, and refrigeration.