An automated purge and trap gas chromatography-mass spectrometry system for the sensitive shipboard analysis of volatile organic compounds in seawater

We developed an automated purge and trap unit connected to a gas chromatogr aph-mass spectrometer for shipboard determination of unstable volatile orga nic compounds in seawater. The device used a small column for the rapid des orption of adsorbed compounds, thus eliminating the need for post-desorptio n cryofocusing. The repeatability (relative standard deviation, RSD; n = 7) was typically < 5%. The detection limits were 0.1-4.3 pM for chloromethane , bromomethane, dichloromethane, iodomethane, dimethyl sulfide, iodoethane, isoprene, bromochloromethane, chloroform, tetrachloromethane, dibromometha ne, bromodichloromethane, iodopropane, chloroiodomethane, dimethyl disulfid e, dibromochloromethane, bromoform, and diiodomethane. To investigate the s tability of seawater samples, we obtained a concentration-time profile of v olatile organic compounds using this method during the incubation of a seaw ater sample with and without the addition of HgCl2 in the dark at 4<degrees >C. We found shipboard determination to be suitable and essential for the d etermination of unstable compounds such as dimethyl sulfide in seawater, as the concentration of dimethyl sulfide increased considerably during the in cubation of a seawater sample both with and without the addition of HgCl2. This method permitted the assessment of numerous naturally produced volatil e organic compounds that are considered to be important for the chemistry o f seawater/atmosphere exchange in the ocean.