Sorption and Extraction

These observations can be qualitatively explained in terms of the constrained-junction theory. If a network is cross-linked in solution and the solvent then removed, the chains collapse in such a way that there is reduced overlap in their configurational domains. It is primarily in this regard, namely reduced chain-junction entangling, that solution-cross-linked samples have simpler topologies, and these diminished constraints give correspondingly simpler elastomeric behavior. 

---

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

Sastre, J., Hernandez, E., Rodriguez, R., Alcobe, X., Vidal, M., and Rauret, G. (2004). Use of sorption and extraction tests to predict the dynamics of the interaction of trace elements in agricultural soils contaminated by a mine tailing accident. Sci. Total Environ. 329, 261—281. 

Although there are direct similarities between MSPD and SPE, the MSPD differs in that it appears to be a mixture of interactions, including partitioning, adsorption, and ion pairing, which makes this an effective method of sorption and extraction. It is possible to elute fractions that contain neutral lipids (hexane), phospholipids (dichloromethane), fatty acids and sterols (acetonitrile), a mixture of phospholipids, amino acids, inositols, mono-, disaccharides, and citric acid (methanol), and finally nucleotides and protein (water). 

Physical adsorption and chemical immobilization techniques were used for the modification of silica gel surface by 1-aminoanthraquinone to produce three modified silica gel phases. These modified phases were studied for their metal sorption and extraction properties. The chemically modified silica phases were applied for selective extraction and preconcentration of Cu(II) and Cr(III) from seawater samples. ... 

Sorption and Extraction of Diluents. In these experiments, the rate at which a suitable diluent is absorbed into a network of known and controlled pore size and the rate at which it can subsequently be extracted are determined (151,154). Of obvious interest is the dependence of the extraction efficiency on the molecular weight Me of the network chains (as a measure of pore size), the molecular weight Md of the diluent, the structure of the diluent (linear, branched, or cyclic), and whether or not the diluent had been present during the end-linking process. 

SH Gehrke, NR Vaid, JF McBride. Protein sorption and recovery by hydrogels using principles of two aqueous phase protein extraction. Biotech Bioeng 58 416-427, 1998. 

Fig. 5. Relationship between the log Koc for phenanthrene sorption and the aliphaticity of humic acids, sequentially extracted from a soil. F-l, F-4, F-7, and F-9 are the first, fourth, seventh, and nineth extracted humic acids, respectively. 0.005, 0.05, and 0.5 pg mL are selected liquid-phase equilbrium concentrations of phenanthrene (Kang and Xing 2005).

Surfactants are selected based primarily on the degree of solubilization. Other factors to be considered include toxicity, biodegradability, surfactant sorption, and surfactant solubility and compatibility with the separation process. Surfactants have the ability to lower the interfacial tension between water and the contaminant by as little as a factor of three to four orders of magnitude. Combined with a sufficient reduction in capillary forces, this allows pumped groundwater theoretically to move the DNAPL toward the recovery or extraction well. This is accomplished by injecting surfactant solution into the contaminated zone. Impacted groundwater characterized by an increase in the concentration of the contaminant is then recovered and treated. 

Apparent hysteresis also may be caused by other phenomena. During the consecutive extractions and dilution steps used as a common technique in desorption studies, weathering of the sorbent may occur, resulting in a possible increase of contaminant sorption and decrease in its release. Degradation of the contaminant induced by physicochemical or biological factors, or a volatilization process leading to a decreased contaminant concentration in solution, are additional factors affecting a true hysteresis result. 

Figures 2-5 show the sorption curves of mass uptake versus time for the extract, O-methylated, O-butylated, and O-octylated extract. Three different experiments are shown in each figure a single integral sorption and two subsequent incremental sorptions. Both the extract and the O-methylated extract required 30 to 150 hours to reach equilibrium, depending on the particular experiment. The O-butylated extract sorbs benzene considerably faster, requiring less than 20 hours to reach equilibrium at all pressures. Finally, the O-octylated extract required less than one hour to reach equilibrium at each pressure.

Figure 6. Sorption-desorption Isotherm for Benzene and Extract of Illinois No. 6 Coal...

Environmental treatments for removing pollutants include in situ degradation with microorganisms and enzymes, use of biofilters, and extraction and sorption of the pollutants. These and other techniques will be covered in this chapter, but for various reasons, the extraction of contaminants is of particular interest primarily because extraction requires no particular pretreatment of the chemical. Air can be injected into the soil around an aquifer and recovered in sorption towers for concentration and removal from the environment. 

A variety of chemical extraction techniques has been developed by soil scientists to determine quantitatively the amount of trace metals bound to soil particles by various mechanisms. Multimechanism sorption has been suggested in order to explain partial irreversibility of radionuclide sorption and increased sorption with exposure time. The five main sorption mechanisms that have been reported are ... 

A two-site model has been used (18) to model cesium transport in soils. In this model a Langmuir-type model, Equation 3,was used to represent surface sorption and a first-order model, Equation 1, was used to approximate interparticle diffusion. Extraction with CaC was used to verify the exchangeable site inventory. 

Lead,J.R., Elamilton-Taylor, J. and Davison, W. (1998) The effect of sequential extractions of suspended particulate matter on trace metal sorption and microbial cell stability. Sci. Total Environ., 209, 193. 

Benzidine, p-aminodiphenyl, is a solid compound that can be extracted from coal tar. It is highly toxic by oral ingestion, inhalation, and skin sorption and is one of the few proven human carcinogens. Its systemic effects include blood hemolysis, bone marrow depression, and kidney and liver damage. 

Determination of the optimum time for which the SPME sorbent will be in direct contact with the sample is made by constructing an extraction-time profile of each analyte(s) of interest. The sorption and desorption times are greater for semi volatile compounds than for volatile compounds. To prepare the extraction-time profile, samples composed of a pure matrix spiked with the analyte(s) of interest are extracted for progressively longer times. Constant temperature and sample convection must be controlled. Stirring the... 

---