Styrene-based columns

In our laboratory at 3M, we similarily have tried to use silica columns to analyze perfluoroether polymers. Severe adsorption was observed, probably caused by extensive use of the column set for other polymers, which may have caused polymer-packing interactions. A styrene-based column custom packed by Jordi Associate was then used. To overcome the tendency of Freon 113 (poor solvent for polystyrene) to collapse styrene columns, the column was initially packed in a less swelling solvent, such as pentane. A void-free column was obtained after displacing pentane with Freon. Figure 3 shows the chromatogram... 

Dejaeger et al. (41) used a styrene-based column in THF with the addition of LiBr to minimize the polyelectrolyte effect of polytrifluoroethyoxyphosphazenes. SEC interfaced with LALLS was also tried despite low detector response caused by a low dn/dc value. The authors also demonstrated that the polyphosphazene counterparts containing no fluorine, that is, polydiphenoxy- and polyaryloxyphosphazenes, follow the universal calibration concept despite their unique backbone structure. 

A method is described for the determination of the preservatives SA and BA in foods (including yogurt, soft drinks, and fruit juices) based on HPLC on a hydrogen-sulfonated divinyl-benzene-styrene copolymer column, isocratic elution with 0.01 N sulfuric acid/acetonitrile (75 25) mobile phase and UV detection at 220 nm (for BA) and 258 nm (for SA). Soft drinks and fruit juices merely require dilution and filtration before injection yogurt samples require treatment with potassium ferricyanide (III) and ZnS04 before analysis. Recovery of SA from yogurt was 95-110% the detection limit was 0.01 mg/kg. The recovery of BA from soft drinks and fruit... 

This paper describes the use of poly(styrene-divinylbenzene) copolymer, PRP-1, as a reverse-phase adsorbent in the assay of the antibiotic aztreonam and related compounds. Comparisons are also made for similar assays using silica-based columns. None of the shortcomings described earlier, associated with bonded phase columns, is observed. In addition to the reverse-phase mode, the PRP-1 columns are tested in ion-pair as well as in size exclusion modes of separation. Superior resolutions are obtained in the reverse-phase chromatography of ionic compounds without the use of lon-palring agents. In addition to the normal adsorption and/or partitioning,... 

A unified theory recently proposed to explain the manner of sorption and the form of sorption isotherm in gas, liquid, and ion-exchange chromatography is presented in some detail. Selectivity in reversed-phase high-pressure liquid chromatography is explored at length. Several chapters deal with characterization of bonded phases, relationship of column-packing structure and performance, variability of reversed-phase packing materials, and the differences between silica-based reversed-phase and poly(styrene-divinylbenzene) columns. A short review is included to cover various approaches used in HPLC to achieve the desired selectivity for resolution of enantiomeric compounds. 

Recently, Veith and Cohen (3) analyzed nylon 6 in TFE using the universal calibration method and peak retention data from narrow PMMA fractions. Silanized silica columns obviate the solvent incompatibility problem of TFE with styrene-based packings and give reproducible results. The accuracy of the calculated nylon 6 molecular weights was cross-checked with an independent end-group analysis (for M ) and intrinsic viscosity measurement (forMJ. 

More recently, columns have been developed where the stationary phase is formed of a porous polymer network inside the capillary. These are called monolithic phases, and have emerged as an alternative to traditional packed bed columns for use in micro-HPLC. They hold many advantages over traditional packed bed columns, being easy to manufacture since the monolith is formed in situ, often via a one-step reaction process, and its properties such as porosity, surface area, and functionality can be tailored. Another major advantage is that they eliminate the need for retaining frits. These columns can be manufactured from a variety of materials, but the most common include sol-gel, methacrylate-based, acrylamide-based, and styrene-based polymeric structures. 

The characteristic structural and technical properties of all surface-aminated styrene/divinylbenzene-based columns mentioned above are summarized in Table 3.2. 

It is important to understand that solubility does not indicate the absence of interactions between the polymer and the stationary phase and insolubility of a polymer does not provide information on interaction effects with the stationary phase. Solubility refers to the binary system of polymer and solvent, while eluent strength refers to the interplay of the interactions among stationary phase, mobile phase, and polymer. As an example, chloroform is a good solvent for poly(methyl methacrylate). However, PMMA is strongly retained on a polar silica column when using chloroform as the eluent, since there is a pronounced interaction of the polar repeating units with the stationary phase. In contrast, on styrene-divinylbenzene-based columns, PMMA clearly elutes in the SEC mode before the injected solvent, indicating that no adsorption of the PMMA onto the stationary phase occurs under these conditions. 

Figure 14.6 AFM tapping mode, phase images of amphiphilic, fluorinated/PECylated styrene-based copolymers. The left hand column shows morphologies of dry films after annealing at 120°. The right hand column shows the same coatings after immersion for 7 days in artificial seawater. The two coatings (A) and (B) differ in the degree of polymerization of the polystyrene (S ) and the relative lengths of...

For styrene, the conversion of monomer per hour rises from —0.1% at 60°C to about 14% at 140°C. Thus, the effect has to be encountered, especially for polymerizations at higher temperatures. Furthermore, when a styrene-based monomer is to be purified by distillation, the addition of inhibitors and distillation at reduced pressure is advisable in order to avoid the distillate from becoming viscous. Another difficulty occurring during distillation is the formation of polymer in the column, which can also be prevented by distilling in vacuo. The initiation of a styrene-based monomer is assumed to involve a (4-1-2) cycloaddition of the Diels-Alder type with a subsequent hydrogen transfer from the dimer to another monomer molecule ... 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

PSS columns for organic eluents PSS SDV columns are based on proven styrene-divinylbenzene type sorbents with improved sorbent characteristics and column technology. 

TosoHaas columns are styrene cross-linked with divinylbenzene (DVB). Columns of similar composition are available from Polymer Laboratories (PL Gel), Waters (Ultrastyragel), Shodex, Jordi (JordiGel), and many others. Columns based on derivatized silica are also available, but are less widely used. 

---