Sorbents polymeric

Although the literature chiefly examines bonded-phase SPE sorbents, there are applications of organic polymers as important phases for SPE. The two most common sorbents are styrene-divinylbenzene (SDB) and activated carbon. These two sorbents do not contain silica but are entirely organic polymers (Fig, 2.9). Typically they have large surface areas (600-1200 m /g), greater capacity than the bonded phases because of higher carbon percentage, and a more hydrophobic surface. They have their major application in the area of reversed-phase SPE. 

The polymeric sorbents are available from several vendors (Hamilton, 3M, and 1ST). In all cases, these sorbents are the styrene-divinylbenzene structure but vary in surface area. Generally speaking the greater the surface area, the greater the capacity of the sorbent for trace organic compounds. Furthermore, the aromatic rings of the matrix network permit electron-donor interactions between the sorbent and ti bonds of the solute, which may further increase analyte-sorbent interactions, which increases the energy of sorption. Thus, the 

The polymeric sorbents have considerably more capacity for polar compounds. For example, Hennion and Pichon (1994) have reported capacities of. 20 to 40 times greater for the polymeric phases than the most hydrophobic 

C-18 phases when isolating polar aromatic compounds from water. This increased capacity is quite important when low detection limits are required. Another advantage of the polymeric sorbents over the silica- ased sorbents is their tolerance for both high and low pH. These polymeric sorbents are stable atpHsfrom 2.0 to 12. 

Examples of the use of these sorbents and their applications will be given in Chapter 7. Finally, a good review of examples of multiresidue extractions of compounds of environmental interest using polymeric and graphitized-carbon sorbents is given by Font and co-workers (1993). 

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Incineration in an approved combustion plant is the preferred method of disposal. Wastewater from succinic acid processes is suitable for biological degradation by activated sludge (188). Polymeric sorbents (189) and ferric chloride treatment processes (190) can also be used for wastes containing... 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

The sorbents that are most frequently used in environmental analysis are Cig-silica based sorbents, polymeric sorbents (usually styrenedivinilbenzene) and graphitized carbon. In order to increase the selectivity of these sorbents, immunosorbents (35, 36) have been developed and used with good results, while recently, molecularly imprinted polymers have started be to used (35, 36). 

An alternative way of eliminating water in the RPLC eluent is to introduce an SPE trapping column after the LC column (88, 99). After a post-column addition of water (to prevent breakthrough of the less retained compounds), the fraction that elutes from the RPLC column is trapped on to a short-column which is usually packed with polymeric sorbent. This system can use mobile phases containing salts, buffers or ion-pair reagents which can not be introduced directly into the GC unit. This system has been successfully applied, for example, to the analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples (99). 

In studies of mice, rats, and dogs, diisopropyl methylphosphonate was rapidly absorbed into plasma (Hart 1976). The plasma data indicate that all three species rapidly absorbed diisopropyl methylphosphonate, although the exact rate was species specific. Although no studies were located regarding human absorption, diisopropyl methylphosphonate is also likely to be absorbed rapidly into the plasma of humans. The ability of porous polymeric sorbents, activated carbon, and dialysis to remove diisopropyl methylphosphonate from human plasma has been studied (McPhillips 1983). The grafted butyl-XAD-4 was found to be the most efficient sorbent for the removal of diisopropyl methylphosphonate from human plasma. Hemoperfusion of plasma over synthetic XAD-4 or butyl-XAD-4 sorbent resin was more efficient than dialysis/ultrafiltration for the removal of diisopropyl methylphosphonate from human plasma the smaller surface of the packed resins provided less area to minimize damage to molecular constituents of the plasma. These methods are useful in reducing diisopropyl methylphosphonate concentrations in the plasma. However, since diisopropyl methylphosphonate and its metabolites are not retained by the body, the need for methods to reduce body burden is uncertain. 

Methods for Reducing Toxic Effects. Little information is available regarding reducing the toxic effects of diisopropyl methylphosphonate following exposure. Recommended treatments include general hygienic procedures for rapid decontamination. The ability of porous polymeric sorbents, activated carbon, and dialysis to remove diisopropyl methylphosphonate from human plasma has been studied. However, since diisopropyl methylphosphonate and its metabolites are not retained by the body, the need for methods to reduce body burden is uncertain. 

Another variation on the luminol CL sensor for N02 was introduced by Collins and Ross-Pehrsson [12] where a solid-phase reagent was positioned below a PMT, across which the air under test is pumped. Of the hydrogel or polymeric sorbents investigated, a Waterlock superabsorbing polymer (hydrogel)... 

TABLE 1.2 Functionalized Neutral Polymeric Sorbents Examples from Literature... 

The complexity of the method in terms of number of steps and solvents needed depends on the sorbent chemistry. The development in a simplified scenario involves running an analyte in several concentrations in multiple replicates and assaying for recovery and performance. This procedure is described in detail for several silica and polymeric sorbents by Wells.42 However, if a number of sorbents are to be evaluated, the process becomes time-consuming if multiple 96-well plates (each with one sorbent packed in all the wells) must be screened separately. This process may take a week or more and consume an analyst s precious time as well. The most plausible solution is to pack different sorbents in the same well plate and use a universal procedure that applies to all of them. An example of such a multisorbent method development plate is the four-sorbent plate recently introduced by Phenomenex demonstrated124 to require only 1 to 2 hr to determine optimal sorbent and SPE conditions. 

Modified silica with a C18 reversed-phase sorbent has historically been the most popular packing material, owing to its greater capacity compared to other bonded silicas, such as the C8 or CN types [22]. Applications of C18 sorbents include the isolation of hydrophobic species from aqueous solutions. The mechanism of interaction with such sorbents depends on van der Waals forces, and secondary interactions such as hydrogen bonding and dipole-dipole interactions. Nevertheless, the main drawbacks of such sorbents are their limited breakthrough volumes for polar analytes, and their narrow pH stability range. For these reasons, reversed-phase polymeric sorbents are also used frequently in environmental applications for the trace enrichment of soluble molecules that are not isolated by reversed-phase sorbents such as C18. 

Classifying polymers in their crosslinked state according to end-use properties, polymer networks include vulcanized rubbers, crosslinked thermosetting materials, protective coatings, adhesives, polymeric sorbents, microelectronics materials, soft gels, etc. Polymer networks in contrast to uncrosslinked polymers,... 

SPE methods with different cartridge packings have been employed for the pre-concentration and clean up of sulfonated azo dyes from waters and soil extracts [110,111], The extraction of solid samples has been carried ont by sonication or Soxhlet extraction and the extracts treated like the water samples. C18 cartridges and columns [111] were used followed by the elution with aqueous organic solvents in the presence of TEA with recovery yields always greater than 65% [93,111], Higher recoveries have been obtained by using C18 columns, pre-conditioned with an ammonium acetate buffer and elnted with methanol [111], The use of styrene-divinylbenzene [93,112], as well as of cross-linked polymeric sorbents with sulfonate functions, was shown to be suitable in the SPE of the more polar componnds [111],... 

Amberlite XAD-2. XAD-2 polymeric sorbent (25) is composed of single resin beads consisting of an agglomeration of numerous minute microspheres (Figure 2). A clue to the efficiency of collection while minimizing reactivity may be found in the structure of the resin. 

Ambersorb carbonaceous adsorbents (Rohm and Haas Company) are a new class of synthetic adsorbents which show interesting collection properties (37,38). The chemical composition is intermediate between that of activated carbon and polymeric sorbents. Ambersorb sorbents are available in various pore sizes and surface areas. 

At present, liquid chromatography is the method of choice for determining residues of quinolone antibacterials in edible animal products (Table 29.6). Separation is generally carried out on nonpolar reversed-phase columns containing octadecyl, octyl, phenyl, or polymeric sorbents. Either methanol or acetonitrile... 

Potential Organic Contamination Associated with Commercially Available Polymeric Sorbents... 

POLYMERIC SORBENTS are frequently used in environmental analytical schemes for the isolation and/or preconcentration of trace organic contaminants from air and water matrices. Commercially manufactured polymeric sorbents such as Amberlite XAD resins, Ambersorb XE resins, Tenax (diphenyl-p-phenylene oxide), and polyurethane foam (PUF) have been used extensively for the collection of trace organic contaminants from ambient air, process streams (i.e., flue gas), and a variety of aquatic matrices including industrial effluents, ground water, surface water, and potable water supplies. Currently, these materials... 

This chapter provides some insight into the chemistry of a number of commonly used polymeric sorbents. Particular focus is placed on the chemical identification of contaminants typically associated with each of the following types of polymeric sorbents Amberlite XAD resins, Ambersorb XE resins, and PUF. Emphasis is placed on the chemical speciation of solvent-extractable organic contaminants present in a number of these sorbents as received from the manufacturer. Both qualitative and quantitative data on a micrograms-per-gram (parts-per-million) basis are provided as determined by combined gas chromatography-mass spectrometry (GC-MS). 

Methylene chloride was selected primarily on the basis of the following criteria (1) It is commonly referred to as the universal solvent or the one used most frequently in the extraction of semivolatile organics sorbed on polymeric sorbent media. Hence, the contaminant chemistry associated with this solvent system would be of the most use to resin users. (2) The physical and chemical properties of methylene chloride make it ideally suited for the extraction of semivolatile organics sorbed on polymeric sorbent media. 

Both Ambersorb XE-340 and XE-348 are members of a carbonaceous polymer product line currently manufactured exclusively by Rohm and Haas. The chemical composition of these sorbents is generally regarded to be intermediate between that ascribed to either activated carbon or a purely polymeric sorbent (9,10). 

PUF, unlike other polymeric sorbents, tends to be a nonhomoge-neous product containing a number of additives and artifacts in variable quantities from lot to lot. Our experience, however, indicates that these contaminants can be sufficiently reduced to permit trace organic analysis by employing a sequential solvent extraction procedure in conjunction with stringent quality control criteria prior to actual use. This observation is consistent with the experience of other investigators who have used flexible foams extensively in analytical environments. 

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