Trace chromatographic analysis of dimethyl sulfoxide and related methylated sulfur compounds in natural waters

Dimethyl sulfoxide (DMSO) occurs in the environment as a result of a number of biogenic and anthropogenic production and emission processes. It is an environmentally significant compound because of its use as a substrate by bacteria and its potential role in the biogeochemical cycle of dimethyl sulfide (DMS), a climatically active trace gas. In this paper, current methods for DMSO determination at nanomolar levels in natural waters, all involving gas chromatography, are reviewed. Direct injection and separation of aqueous DMSO offers a simple and fast application, but exhibits limited sensitivity due to limitation on injection volumes. So far, most authors have preferred DMSO reduction and subsequent analysis of the evolved DMS by purge-and-trap preconcentration and flame photometric detection. Several reducing agents have been used, though some require cumbersome procedures or are very sensitive to operational conditions. The common algal component dimethylsulfoniopropionate (DMSP) acts as an interference in some reduction methods and, therefore, either DMSP elimination prior to DMSO analysis or correction a posteriori is required. DMSO can be analyzed along with DMS, methanethiol, dimethyl disulfide and DMSP in the same water sample, either sequentially or separately, so that comprehensive speciation of methylated sulfur is obtained. Owing to the biological activity of DMSO, appropriate water sampling and handling procedures must be applied. Acidification and freezing appear to be suitable for aqueous DMSO storage, although immediate analysis in the field is always preferable. Future directions of DMSO determination in aquatic environments are suggested.