Particulate-matter extracts, fractionating

The simplest approach to the collection and subdivision of organic materials in seawater is to use some physical or chemical means of removing one fraction from solution or suspension. The techniques vary, from simple filtration to collect particulate matter, to chemical methods, such as solvent extraction and coprecipitation. With each of these methods, the analyst must know the efficiency of collection and exactly which fraction is being collected. Very often the fraction is defined by the method of collection two methods... 

Finally, completely equating the "mobile phase with solvent (e.g. pyridine) extractable "bitumen in coal ignores the potential presence of colloidal particulate matter in the pyridine extracts as well as possible solvent-induced scission of weak chemical bonds. Furthermore, the solvent-extractable fraction may well include macromolecular components, such as resinites. 

A portion (10.2 cm x 17.8 cm) of each RSP sample was sequentially extracted in a Soxhlet apparatus with cyclohexane, di-chloromethane and acetone, (8 hr. for each solvent) in the order given. A more complete extraction of the organic compounds present in particulate matter is achieved and a partial separation of the organic compounds into non-polar, moderately polar and polar fractions is obtained by this method. The volume of each extract was reduced to 10.0 ml using a rotary evaporator. The samples were then stored in a freezer at -15 C until further analysis. Weights of extracts were determined by weighing duplicate 100 yl aliquots of each, taken to dryness on a slide warmer (40 C), on a Cahn Electrobalance. 

Throughout this chapter, we cite examples of the use of the NIST Standard Reference Material SRM 1649, which is referred to as Air Particles or Urban Air Particulate Matter, (a) to validate analytical procedures for determination of PAHs and PACs in samples of complex mixtures of particulate matter in ambient air and (b) for laboratory intercomparisons of methodologies for bacterial bioassays and bioassay-directed fractionations of organic extracts of such mixtures (e.g., see Claxton et al., 1992a Lewtas et al., 1990a, 1992 and May et al., 1992). 

Chuang, J., M. Nishioka, and B. Petersen, Bioassay-Directed Fractionation of the Organic Extract of SRM 1649 Urban Air Particulate Matter, Int. J. Environ. Anal. Chem., 39, 245-256 (1990). 

Solvent extraction of the sample is also frequently used in the analysis of particulate matter. Through the appropriate choice of solvents, the organics can be separated into acid, base, and neutral fractions, polar and nonpolar fractions, and so on. This grouping of compounds according to their chemical properties using extraction techniques simplifies the subsequent analysis. Each fraction can then be analyzed by GC-MS, with the GC retention time and the mass spectrum used for identification and measurement. 

The analytical methodology complicates determining the particulate fraction of POPs. A portion of the compound in particulate matter appears freely exchangeable with its vapor phase, while another portion is strongly sorbed or occluded (Pankow, 1988 Pankow and Bidleman, 1991 1992). Most analytical schemes for particulate matter on filters call for extraction with dichloromethane, acetone-dichloromethane, or toluene, and these solvents may access some of the "non-exchangeable" POPs (Ligocki and Pankow, 1989 Pankow and Bidleman, 1991 Rounds et al., 1993). 

Iwatsuki, M., T. Kyotani, and K. Matsubara. 1998. Fractional determination of elemental carbon and total soluble and insoluble organic compounds in airborne particulate matter by thermal analysis combined with extraction and heavy liquid separation. Anal. Sci. 14 321-326. 

In addition to the need to monitor known problematic compounds, newer compounds are being identified as potential threats to humans and as such need to be monitored in the atmosphere. For example, researchers reported (10) that several chemical and instrumental analyses of HPLC fractions provided evidence for the presence of /V-nitroso compounds in extracts of airborne particles in New York City. The levels of these compounds were found to be approximately equivalent to the total concentrations of polycyclic aromatic hydrocarbons in the air. Since 90% of the N-nitroso compounds that have been tested are carcinogens (10), the newly discovered but untested materials may represent a significant environmental hazard. The procedure involved collecting samples of breathable, particulate matter from the air in New York City. -These samples were extracted with dichloro-methane. Potential interferences were-removed by sequential extractions with 0.2 N NaOH (removal of acids, phenols, nitrates, and nitrites) and 0.2 N H2S04 (removal of amines and bases). The samples were then subjected to a fractional distillation and other treatments. Readers interested in the total details should consult the original article (10). Both thin-layer chromatography (TLC) and HPLC were used to separate the compounds present in the methanolic extract. 

For the purposes of this method, a water sample is defined as a single phase system that is primarily clear water but may contain very small amounts of floating, suspended and settled particulate matter. Multiple phases should not be present (see Section 8.4). Approximately 1 L of the water sample is spiked with the internal standard solution and filtered to separate the aqueous and particulate fractions. The filtered aqueous fraction is extracted with methylene chloride using a separatory funnel or continuous liquid-liquid extractor. The particulate fraction is extracted with toluene in a SDS extractor. The extracts of the two fractions are then combined for cleanup. 

Terrestrial materials (river sediments, lake sediments, and urban particulate matter) appear to have between 50% and 70% exchangeable Pb and Zn while marine sediments contain very little exchangeable metal but appreciably more reducible and much more residual Pb and Zn (Kersten and Forstner, 1995). This may not be too surprising as exchangeable metals are released once freshwater mixes with salt water and redistribution in the marine environment results in some precipitated phases (carbonates, Fe/Mn oxyhydroxides) and the relative increase in the lithogenic fraction. In future, the solid-phase identification techniques should be used to classify the sediments that are to be subjected to selective extraction techniques for the purpose of understanding the heavy metal phase associations. 

Water samples may contain appreciable amounts of particulate matter, dissolved organic carbon, or colloidal material and all of these may form associations with the analytes and affect their recoverability. For these reasons, discrepancies may arise between the concentrations of analytes determined by liquid extraction and those obtained by sorption on polyurethane or XAD resins (Gomez-Belinchon et al. 1988). Empirical procedures have been developed (Landrum et al. 1984) for fractionating samples to assess the relative contribution of the associations of xenobiotics with the various organic components, while sediment traps for collection of particulate matter have been extensively used in investigations in the Baltic Sea where appreciably turbid water may be present (Nat et al. 1992). 

Although the globally distributed DDT is a very well investigated xenobiotic regarding the environmental occurrence and behaviour, detailed information about the fate of DDT in the bound residues fraction is very limited. Already in 1977 Lichtenstein et al. (1977) reported the formation of bound 14C-labelled DDT on agricultural soil accompanied by a drastically reduced insecticidal activity of the associated proportion. Also recent studies confirmed the decrease of DDT toxicity with time after application to soils as a result of less bioavailibility due the incorporation into the non-extractable particulate matter (Robertson and Alexander 1998). For a better understanding of the processes leading to these observations more information is required about the incorporation of DDT residues into the non-extractable particulate matter not only of soils but also of particulate matter within the aquatic environment. 

The association of DDT-related pollutants to the non extractable matter of sediments from the Teltow Canal has been reported recently (Chapter 4.3.2 and Schwarzbauer et al. 2003a). This study was primarily initiated to quantify concentrations of bound 2,2-bis(chlorophenyl)-l,l,l-trichloroethane (DDT) residues in order to obtain further information about the fate of DDT-derived compounds within the particulate matter of the aquatic environment. Generally, the distribution of the bound DDT-related compounds was found to differ distinctly from the distribution within the extractable fraction (Schwarzbauer et al. 2003a). 

SPE has been used to estimate the amount of freely dissolved PAHs versus DOM-associated and particulate-associated PAHs. Glass fiber filters used to remove particulate matter from water samples before extraction can also retain some DOM-associated PAHs. It is largely thought that DOM-associated PAHs will pass through reverse-phase SPE cartridges allowing for the measurement of the freely-dissolved fraction, however, some DOM-associated PAHs are retained... 

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