Organic compounds from aqueous phase

Extraction of organic compounds from aqueous phase... 

Extensive studies have been conducted for the extraction of organic compounds from aqueous phase with ILs, depending on the affinity between hydrophobic ILs and organic solutes. The extraction mechanism includes ion exchange, hydrogen bond. Van der Waals... 

Another relatively new SPE approach originally developed for the analysis of volatile organic compounds in environmental samples is solid-phase microextraction (SPME). This technique has gained acceptance for a wide variety of additional applications for the isolation of organic compounds from aqueous solu-... 

Stir bar sorptive extraction (SBSE), an approach theoretically similar to SPME, was recently introduced [141] for the trace enrichment of organic compounds from aqueous food, biological, and environmental samples. A stir bar is coated with a sorbent and immersed in the sample to extract the analyte from solution. To date, reported SBSE procedures were not usually operated as exhaustive extraction procedures however, SBSE has a greater capacity for quantitative extraction than SPME. The sample is typically stirred with the coated stir bar for a specified time, usually for less than 60 minutes, depending on the sample volume and the stirring speed, to approach equilibrium. SBSE improves on the low concentration capability of in-sample solid-phase microextraction (IS-SPME). 

Supercritical fluids such as carbon dioxide can be used as solvents to extract organic compounds from aqueous solutions. In order to achieve recoveries of these products often in low concentration, cosolvents as methanol or other alcohols have been added to improve the solubility and the selectivity of the primary fluid. To optimize the extract recovery, the knowledge of phase equilibria of the ternary system carbon dioxide-methanol-water is required at different temperatures and pressures. 

Determination of the thermodynamic parameters for the transfer of non-polar organic compounds from aqueous to non-aqueous phases has been extensively used to estimate the free energy changes involved in hydrophobic interactions (Nemethy, 1967 Jencks, 1969). The experimental difficulties involved in the accurate determination of solubilities together with the approximations necessitated by limiting the measurements to simple organic compounds are the inherent disadvantages of this model. 

D. L. Mayer and J. S. Fritz, Semi-micro solid-phase extraction of organic compounds from aqueous and biological samples,/. Chromatogr. A, 773,189,1997. 

SPME was first reported by Pawliszyn and coworkers in 1990." " This method can be used for the extraction of organic compounds from aqueous samples or from a gas phase (headspace-SPME). SPME is by nature an equilibrium technique, based on the partitioning of the solutes between the sUicone phase and the aqueous and/or gas matrix. The device employed for SPME is formed by a thin, fused sUica fiber with a chemically bonded organic film on its surface (Figure 2.12). 

When SPME is applied to analysis of water samples, the sample is placed in a vial with a cap that contains a septum. In order to extract the analytes from the sample, the sheath is pushed through the septum and the plunger is lowered, forcing the hber into the vial, where it is immersed into the aqueous sample or its headspace. Then the SPME hber absorbs organic compounds from the phase that is in contact with it unhl equilibrium is achieved. 

A small, 20 X 1 mm ID, monolithic rod, obtained by the polymerization of 80% tec/i-DVB in a mixture of dodecanol and toluene, was employed for the solid-phase extraction of polar organic compounds from aqueous solutions [415]. It was demonstrated again that by maintaining constant dilution of the monomer and changing only the weight percent ratio of toluene to dodecanol from 2 58 to 10 50, it is possible to increase the surface area of the sorbent from 188 to 348m /g and to reduce the mean pore diameter... 

Insofar as the derivatization can be considered one of the stages of sample preparation for chromatographic analysis, it can be combined with other procedures, for instance, the preconcentration of traces of analytes. For example, the yield of solid-phase extraction or microextraction of organic compounds from aqueous solutions with modified silica gels is better for more hydrophobic substances the preliminary conversion of acidic compounds into suitable derivatives is recommended. ... 

Activated carbon, by comparison, is the workhorse of the porous carbons. Chapter 8 initially examines the chemistry and mechanisms of adsorption of inorganic and organic compounds from aqueous solution, and then moves on to summarize the most important of gas- and liquid-phase applications. 

The use of vegetable oil for remediation of organic contaminants in an aquifer or unsaturated zone has been smdied at Pacific Northwest Laboratory. The oil strips organic compounds from the aqueous phase or particulate matter and is then pumped out for recovery. In addition, the oil can be used as a carbon source by microorganisms, hence encouraging in situ bioremediation. The technology has not proceeded beyond bench-scale testing and is not commercially available. 

Rohm and Flaas Company has developed Amberlite polymeric adsorbent resins that can be used to remove organic compounds from contaminated groundwater, aqueous wastes, and vapor-phase wastes. Amberlite XAD-4 is a crosslinked polystyrene-type polymer. It is hydrophobic and has no ionic functional groups incorporated into its resin structure. The material is most useful in removing low-molecular-weight organic substances from aqueous systems. Amberlite XAD-4 has been commercially available since the 1970s. 

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