Continuous underway measurements of dimethyl sulfide in seawater by purge and trap gas chromatography coupled with pulsed flame photometric detection

Abstract

In this study, a conventional purge and trap (PT) system was modified with gas chromatography coupled with pulsed flame photometric detection (GC-PFPD) to achieve long-term continuous shipboard underway measurements of trace-level dimethyl sulfide (DMS) in unfiltered seawater. This PT system is automated, time-efficient and electronically temperature controlled. A complete analytical cycle for each sample only requires 8.5min. The critical aspects of the PT-GC-PFPD system were evaluated, and sharp peaks were observed for nanomolar levels of DMS with a low limit of detection (LOD) of 0.05nmolL−1. Unfiltered seawater samples were continuously supplied to the system because small deviations were observed in the responses between filtered and unfiltered seawater samples (ranging from 0.7% to 4.7%). Moreover, during 9days of continuous in-situ observations, a 6% deviation in the standards was observed, indicating that this system is reliable and stable. The successful application of this system in a field study suggested that the proposed DMS analysis method would significantly facilitate data collection in the field. In addition, dimethylsulfoniopropionate (DMSP) was also detected by this system after conversion to DMS. The required modifications are affordable and can be easily performed by laboratories that have traditional, non-commercial, purge and trap systems.