Polystyrene-divinylbenzene-copolymer

A macroporous polystyrene-divinylbenzene copolymer is produced by a suspension polymerization of a mixture of monomers in the presence of water as a precipitant. This is substantially immiscible with the monomer mixture but is solubilized with a monomer mixture by micelle-forming mechanisms in the presence of the surfactant sodium bis(2-ethylhexylsulfosuccinate) (22). The porosity of percentage void volume of macroporous resin particles is related to percentage weight of the composite (50% precipitant, 50% solvent) in the monomer mixture. 

A macroporous polystyrene-divinylbenzene copolymer, produced by copolymerizing a mixture of styrene and divinylbenzene, is dissolved in an organic liquid such as t-amyl alcohol or isooctane, which is a solvent for monomers. This solvent is unable to substantially swell the resulting copolymer. Macroporous cation-exchange beads are also produced from these macroporous copolymers (25,26). 

A novel cross-linked polystyrene-divinylbenzene copolymer has been produced from suspension polymerization with toluene as a diluent, having an average particle size of 2 to 50 /rm, with an exclusive molecular weight for the polystyrene standard from about 500 to 20,000 in gel-permeation chromatography. A process for preparing the PS-DVB copolymer by suspension polymerization in the presence of at least one free-radical polymerization initiator, such as 2,2 -azo-bis (2,4-dimethylvaleronitrile) with a half-life of about 2 to 60 min at 70°C, has been disclosed (78). 

A pivotal step in the analytical process is sample preparation. Frequently liquid-liquid extractions (LLEs) are used. Solvents, pH, and multiple back extractions are all manipulated to increase selectivity and decrease unwanted contaminants before injection on the GC system. Solid phase extraction (SPE) is more convenient than it used to be because of an increase in commercially available SPE columns. SPE columns are packed with an inert material that binds the drug of interest, allowing impurities to pass through. As with LEE, solvent choices and pH affect retention and recovery. There are three commercially available types of SPE columns, diatomaceous earth (which uses the same principles as LLE), polystyrene-divinylbenzene copolymer, and mixed mode bonded silica (Franke and de Zeeuw, 1998). 

Table 5.6 The number a of solvent molecules sorbed per phenyl group and the limiting Flory -Huggins parameter x0 for polystyrene-divinylbenzene copolymers- solvent systems (Errede 1989)...

There are two main classes of polymeric support utilized in the preparation of stationary phases for all modes of chromatography, namely silica and polystyrene-divinylbenzene copolymer. For simplicity, from this point on, the former will be referred to as silica and the latter class as polymeric. 

High Performance Size Exclusion Chromatography. The Hewlett-Packard 1090 liquid chromatograph was used with the HP 1040 diode array or HP 1037A refractive index (and HP 3392 integrator) detectors. A fifty A (5 mm, 300 x 7 mm) Polymer Laboratories PL gel (polystyrene-divinylbenzene copolymer gel) column was used and standards were as described in Chum et al. (13). Tetrahydrofuran solutions of oil and oil fractions were analyzed. 

The majority of reversed-phase methods have been developed on covalently modified silica gel and the most popular stationary phase is octade-cylsilyl silica (ODS, Cig). Polymeric supports, such as functionalized polystyrene-divinylbenzene copolymers (MacBlane et al., 1987), are particularly useful when mobile phases of higher pH are required because of their resistance to degradation in alkaline solutions. The main drawback of polymeric supports is their reduced column efficiencies and their lower mechanical resistance to high pressures compared with silica gel. 

Non-polar supports like polystyrene/divinylbenzene copolymers or carbon are also used as column materials. Alumina is polar and acidic while TiOi, and zirconia are much more neutral. They all have good aqueous stability compared to silica. Normal phase chromatography is restricted to the separation of stereochemical isomers, diastereomers, low molecular weight aromatic compounds and functionalized long chain aliphatic compounds. 

Pietrzyk et al. studied the effect of solute ionization on the chromatographic retention. As stationary phase the polystyrene-divinylbenzene copolymer XAD was used. One of the model compounds was nicotine, for which the retention at various pH of the mobile phase was determined. 

A comparison study of Cig-bonded silica cartridges and polystyrene-divinylbenzene copolymer membrane absorption disks showed that the latter were the more effective for SPE of phenols at the 0.5 ppb concentration levels (70-98% recoveries), whereas the Cis cartridges were preferable for higher concentration levels (10 ppb) because smaller sample and solvent volumes were required and analysis time was therefore shorter. End analysis was by LC-ELD, with a phosphate buffer-acetonitrile-methanol mixture as mobile phase and coulometric detection at +750 mV. A study was carried on the preconcentration step of phenol, < -, m-, p-methylphenol, < -, m-, p-chlorophenol, 2,5-, 2,6-dichlorophenol, catechol (42), resorcinol (20) etc., at 0.5 and 5 figL concentrations. SPE utilizing a divinylbenzene-hydrophilic methacrylate copolymer gel showed recoveries better than... 

Extraction and derivatization supported on a neat polystyrene-divinylbenzene copolymer adsorbent material provided several advantages over conventional sample preparation techniques, including less solvent consumption, less time-consuming steps in the method, low detection limits, excellent repeatability, and no loss of volatiles. ... 

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