Preparation of lipophilic organic seawater concentrates

Research since the late 1960s into the extent and nature of pollution of the marine environment by anthropogenic chemicals has led to the development of analytical techniques for qualitative and quantitative determinations of traces of organic contaminants in organisms, suspended particles, sediments and water. 

The most conspicuous organic contaminants of seawater are organochlorine compounds (Broman et al., 1991), fossil hydrocarbons and their oxidation products Ehrhardt and Bums, 1993), linear alkylbenzenes, alkylphenols (Marcomini et al, 1990 Blackburn and Waldock, 1995), and phthalate esters Waldock, 1983). Concentration procedures for these lipophilic substances are described here. However, the analyst should be aware of the fact that contaminants are not the only lipophilic chemicals likely to be present in seawater. A large number of recently biosynthesised, as well as man made chemicals not listed above, will also be concentrated by these methods. 

Lipophilic organic compounds in seawater usually occur at minute concentrations. The high sensitivity of modem analytical instruments would, in principle, permit analyses of the amounts present in small volume water samples. However, contamination of the sample by substances adhering to the surfaces of water samplers or laboratory glassware, by solvents, reagents, gases, etc., becomes a severe problem at ultratrace levels of analytes usually present in seawater. 

Numerous attempts have been made to overcome the limitations of small sample size and to accumulate lipophihc organic compounds from large volumes of water. Batch extractions with water-immiscible solvents have been described by Gaul and Ziebarth (1984) and Theobald et al. (1990). However, with increasing sample volume the volume of the liquid extractant must also increase because of its non-zero solubility in seawater. Thus, the 

After extraction, lipophilic compounds are partitioned into n-hexane. More hydrophilic high relative molecular mass components of DOM remain in the more polar primary extract. If necessary, organic bases and acidic substances may be removed from the hexane phase by liquid extraction with aqueous acids and bases, respectively. 

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Technical grade preparations of mirex consists of 95.19% mirex and less than 2.58 x 10 % contaminants, mostly kepone CioClioO. Mirex is comparatively soluble in various organic solvents, such as benzene, carbon tetrachloride and xylene, with solubilities ranging from about 4000.0 to 303,000.0 mg/L. However, mirex has a very low solubility in water, not exceeding 1.0(xg/L in freshwater or 0.2 xg/L in seawater. In biological systems, mirex lipophilicity would account for the high concentrations observed in fatty tissues and reserves. 

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