Low molecular weight halocarbons in the Humber and Rhine estuaries determined using a new purge-and-trap gas chromatographic method

A number of chlorinated and brominated low molecular weight hydrocarbons (halocarbons) have been measured in and adjacent to the North Sea estuaries of the Humber and the Rhine. The measurements have been carried out using a newly constructed purge-and-trap sample work-up system coupled to megabore gas chromatography with electron capture detection. The results show that whereas the Humber is a pronounced source of the anthropogenic halocarbons carbon tetrachloride and perchloroethylene, the input from the Rhine into the North Sea of these compounds is more modest. Some halocarbons normally considered as mainly or even exclusively of natural origin are released from the two investigated estuaries into the North Sea. A distinct patch of high concentrations of the naturally produced compound bromoform was observed in the southwestern North Sea. The results have also been used to examine some of the halocarbons for common sources.

Quantification of oxygenated volatile organic compounds in seawater by membrane inlet-proton transfer reaction/mass spectrometry

The role of the ocean in the cycling of oxygenated volatile organic compounds (OVOCs) remains largely unanswered due to a paucity of datasets. We describe the method development of a membrane inlet-proton transfer reaction/mass spectrometer (MI-PTR/MS) as an efficient method of analysing methanol, acetaldehyde and acetone in seawater. Validation of the technique with water standards shows that the optimised responses are linear and reproducible. Limits of detection are 27 nM for methanol, 0.7 nM for acetaldehyde and 0.3 nM for acetone. Acetone and acetaldehyde concentrations generated by MI-PTR/MS are compared to a second, independent method based on purge and trap-gas chromatography/flame ionisation detection (P&T-GC/FID) and show excellent agreement. Chromatographic separation of isomeric species acetone and propanal permits correction to mass 59 signal generated by the PTR/MS and overcomes a known uncertainty in reporting acetone concentrations via mass spectrometry. A third bioassay technique using radiolabelled acetone further supported the result generated by this method. We present the development and optimisation of the MI-PTR/MS technique as a reliable and convenient tool for analysing seawater samples for these trace gases. We compare this method with other analytical techniques and discuss its potential use in improving the current understanding of the cycling of oceanic OVOCs.