Organic Compounds Sorbed Onto Solids

4 Organic Compounds Sorbed Onto Solids. - Coke on Al-MCM-41, and 

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In natural waters, arsenic may exist as one or more dissolved species, whose chemistry would depend on the chemistry of the waters. Over time, arsenic species dissolved in water may (1) interact with biological organisms and possibly methylate or demethylate (Chapter 4), (2) undergo abiotic or biotic oxidation, reduction, or other reactions, (3) sorb onto solids, often through ion exchange, (4) precipitate, or (5) coprecipitate. This section discusses the dissolution of solid arsenic compounds in water, the chemistry of dissolved arsenic species in aqueous solutions, and how the chemistry of the dissolved species varies with water chemistry and, in particular, pH, redox conditions, and the presence of dissolved sulfides. Discussions also include introductions to sorption, ion exchange, precipitation, and coprecipitation, which have important applications with arsenic in natural environments (Chapters 3 and 6) and water treatment technologies (Chapter 7). 

Sorption of organic contaminants onto aquifer solids is frequently described as a partitioning process, where the hydrophobic organic compound partitions into natural organic material associated with the aquifer solids [8]. Sorption can be characterized as either an equilibrium or rate-limited phenomenon. Equilibrium sorption can be modeled as either a linear or non-linear process. Equilibrium sorption may be assumed when the flow of groundwater and other processes affecting contaminant transport are slow compared to the rate of sorption. In this event the sorption of the contaminant can be considered instantaneous. If we assume equilibrium sorption, the relationship between sorbed and aqueous contaminant concentrations may be described by a sorption isotherm. 

Sample analysis based on sorption onto SPE sorbents followed by elution with organic solvent is the basis of the majority of SPE methods. However, the use of fibers to sorb organic compounds directly from solution was developed by Pawliszyn and co-workers (Arthur and Pawliszyn, 1990), and devices are commercially available from Supelco (see Chapter 12 for a description of the method). The adsorbed compounds may be directly desorbed into the GC without a solvent peak by simply heating the fiber in the inlet of the gas chromatograph. Solid-phase microextraction (SPHE) has mainly been used... 

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