Gas Chromatographic Trace-Level Determination of Volatile Organic Sulfides and Selenides and of Methyl Iodide in Atlantic Surface Water

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Abstract
The concentration of the sulfur compounds dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and carbon disulfide (CS2) as well as of methyl iodide (CH3I) was determined in surface sea water of the Atlantic Ocean from 30°S to 45°N during an expedition with the German research vessel 'FS Polarstern' using a purge and trap/gas chromatographic system equipped with a flame photometric and an electron capture detector. The most abundant sulfur compound was DMS with a mean concentration of 55 ng S/l. DMDS and CS2 could be detected in 14 and 56 out of a total number of 100 sea water samples with concentrations up to 14.7 ng S/l and up to 10.7 ng S/l, respectively. This is the first time that DMDS could be quantified in a number of sea water samples. CH3I was determined in all samples with a mean of 0.6 ng I/l. In three Atlantic sea water samples dimethyl selenide (DMSe) was detected for the first time (concentration range, 1–5 ng Se/l). Its presence was verified by means of an atomic emission detector. DMSe was the only volatile selenium compound found. Contrary to CS2, the concentrations of CH3I and especially of DMS and DMDS are related to the levels of marine primary production. In agreement with this, the DMS concentrations correlated well with those of dimethyl sulfonium propionate (DMSP). However, no clear relationship between CH3I and DMS could be found, indicating a different pathway of biological production.