DETERMINATION OF TRACE LEVELS OF DIMETHYLSULFOXIDE (DMSO) IN SEAWATERAND RAINWATER

A procedure for the trace analysis of dimethylsulfoxide (DMSO) in seaw ater and other aqueous solutions has been developed. The method is bas ed on reduction of DMSO to dimethyl sulfide (DMS) by titanium trichlor ide (TiCl3) and the subsequent measurement of DMS by gas chromatograph y. As little as 1 picomole of DMSO could be detected by the method yie lding a detection limit of 1 nM for a 1 ml sample. Precision for most natural water samples with 5-20 nM DMSO was better than 10%. Water sam ples stored in the dark and either frozen (-20-degrees-C) or acidified (0.05 M HCl; 4-degrees-C) showed no significant losses or contaminati on over a 3 week period. The reduction reaction was selective for DMSO , in that other sulfur compounds including methionine, homocysteine, c ysteine, glutathione, dimethyl sulfone, methionine sulfoxide, dimethyl sulfoniopropionate (DMSP) and S-methylmethionine did not yield DMS. Ho wever, a required basification step in the procedure caused conversion of DMSP to DMS, therefore parallel samples without TiCl3 were used to correct for dissolved DMSP or DMS in the solution analyzed. Tests sho wed that DMSP was the only compound which yielded DMS during the basif ication step. Significant analytical blanks were observed if precautio ns were not taken to minimize air contamination of glassware, reagents and the analyte solution. Detailed information on how to minimize bla nks is given. Using the method we measured seawater DMSO concentration s ranging from 1 to 13 nM and rainwater DMSO concentrations ranging fr om 1 to 26 nM. A preliminary incubation experiment with water from Mob ile Bay, Alabama indicated that added DMSO (50 nM) was consumed over a 5 day period. The method should be useful in studies of DMSO and DMS biogeochemistry.