Sampling, filtration and storage

Great care is required if truly representative samples of seawater are to be collected for DOC determinations (see general comments about sampling elsewhere in this volume, e.g., Chapters 1, 2 and 15). A major potential problem is contamination. Sources of contamination can be very variable, and clearly materials which come into direct contact with samples must be free of soluble organic materials specific approaches to cleaning are described below. A particular problem for DOC samples is contamination by volatile water soluble compounds such as ketones and alcohols, which may be in common use in laboratories, and can be introduced through the vapour phase from the atmosphere into samples. It is sensible to limit exposure of the sample to the laboratory atmosphere and to have dedicated areas for this type of work away from potential contamination sources. 

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In recent years the study of mobile soil and groundwater colloids has received considerable attention because of concerns that such a vector may enhance the mobility of strongly sorbing contaminants, a process that is often referred to as facilitated transport. 15-16 However, our ability to predict colloid movement and deposition is often confounded by the complexities of surface interactions in such dynamic, unstable systems. The lack of universally accepted analytical techniques and failure to realize instrumental limitations have made it difficult to compare and critically evaluate the results of different studies. Artifacts associated with ground-water sampling, filtration, and storage, and the dilute nature of most soil and ground-water suspensions further hamper characterization efforts.17-21... 

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