Polystyrene HPLC matrices

Fig. 5-7. Plot of flow rate versus column pressure for a series of polystyrene HPLC matrices (A) 100 A,...

Gel permeation ehromatography (GPC)/normal-phase HPLC was used by Brown-Thomas et al. (35) to determine fat-soluble vitamins in standard referenee material (SRM) samples of a fortified eoeonut oil (SRM 1563) and a eod liver oil (SRM 1588). The on-line GPC/normal-phase proeedure eliminated the long and laborious extraetion proeedure of isolating vitamins from the oil matrix. In faet, the GPC step permits the elimination of the lipid materials prior to the HPLC analysis. The HPLC eolumns used for the vitamin determinations were a 10 p.m polystyrene/divinylbenzene gel eolumn and a semipreparative aminoeyano eolumn, with hexane, methylene ehloride and methyl tert-butyl ether being employed as solvent. 

Starting from the corresponding hydroxymethyl-benzocrown, it has been possible to generate the immobilized system (186) by reacting the above precursor with chloromethylated polystyrene (which is available commercially as Merrifield s resin). Typically, systems of this type contain a polystyrene matrix which has been cross-linked with approximately 1-4% p-divinylbenzene. In one study involving (186), a clean resolution of the alkali metal halides was achieved by HPLC using (186) as the solid phase and methanol as eluent (Blasius etal., 1980). In other studies, the divalent alkaline earths were also separated. 

Besides choosing the appropriate Ab, the assay method can be designed or manipulated to improve assay specificity using (a) protein precipitation, (b) liquid/liquid or solid-phase extraction, (c) HPLC separation of the analyte from the interfering compounds, (d) sample dilution with buffer or control matrix, or (e) an affinity solid phase (e.g., antibody-coated microtiter plate or polystyrene beads) to capture the analyte followed by wash steps. Affinity-purified antibodies and protein blockers are used in EIA to decrease nonspecific binding in plate assays. Increasing incubation time to reach equilibrium also improves binding specificity. 

Hypercrosshnked polystyrenes proved to be unique HPLC column packing materials (Chapter 13), adsorbents for sofid-phase extraction (Chapter 14), hemosorbents (Chapter 15), and a matrix for hypercrosslinked ion-exchange resins (Chapter 16). 

Despite all of these advancements, there still exist several limitations in the synthesis of peptide-polymer conjugates. They include quantity, which is limited to the milligram scale, purification, and characterization. For example, conjugates incorporating hydrophobic polymers, such as polystyrene (PS), are especially difficult to purify and characterize by typical techniques, such as reversed-phase high-performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). 

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