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

Abstract

We developed an automated purge and trap unit connected to a gas chromatograph-mass spectrometer for shipboard determination of unstable volatile organic compounds in seawater. The device used a small column for the rapid desorption of adsorbed compounds, thus eliminating the need for post-desorption 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, dibromomethane, bromodichloromethane, iodopropane, chloroiodomethane, dimethyl disulfide, dibromochloromethane, bromoform, and diiodomethane. To investigate the stability of seawater samples, we obtained a concentration-time profile of volatile organic compounds using this method during the incubation of a seawater sample with and without the addition of HgCl2 in the dark at 4°C. We found shipboard determination to be suitable and essential for the determination of unstable compounds such as dimethyl sulfide in seawater, as the concentration of dimethyl sulfide increased considerably during the incubation of a seawater sample both with and without the addition of HgCl2. This method permitted the assessment of numerous naturally produced volatile organic compounds that are considered to be important for the chemistry of seawater/atmosphere exchange in the ocean.