Oddvar Arnfinn Aune

Monosized stationary phases for chromatography

Abstract Polymer particles with a highly monodisperse particle size distribution were produced by a two-step microsuspension method. This process is based on the activation of monosized polymer seed particles by the introduction of a low-molecular-weight material, which leads to a large increase in the monomer swelling capacity of the seed particles. The versatility of the process allows the preparation of polymer monosized compact or macroporous particles of predetermined particle size in the range 1–100 μm and with application of a wide selection of polymeric materials. Underivatized, rigid, porous particles were developed for size-exclusion chromatography in organic solvents. The uniform packing that may be achieved with monosized particles has resulted in chromatographic columns with unusual efficiency and separation capacity. By coating the particle surface with a hydrophilic cross-linked polymer, supports for aqueous phase ion-exchange and size-exclusion chromatography may be produced.

Thermodynamics of Swelling of Polymer, Oligomer and Polymer-Oligomer Particles. Preparation and Application of Monodisperse Polymer Particles.

The treatment of the equilibrium distribution in various polymer-monomer or polymer-mixed solvent systems has most often been based upon the classical Flory-Huggins lattice theory and the extension of this theory by Morton to include the interfacial energy. Further developments of these theories have included the swelling of polymer particles with mixtures of different monomers, systems in which the continuous phase (water in the case of aqueous dispersions) is present in the monomer and polymer phases, and the swelling of oligomer and oligomer-polymer particles. Ugelstad et al. have shown experimentally and theoretically that oligomer particles and oligomerpolymer particles in aqueous dispersions are capable of absorbing monomer to an extent that are orders of magnitude higher than for pure polymer particles. This has led to development of emulsion polymerization procedures which allow preparation of highly monosized large particles in the range of 1–50 μm in diameter. Such particles have up to now found industrial application in liquid chromatography. The particles are furthermore used as standards for blood cell counters. Hydrophilic monosized particles prepared by the new methods are utilized in different immunoassays where they have been found to possess advantageous properties. The monodisperse particles have also founded the basis for the preparation of monosized magnetizable microspheres which have been applied for cell separation.

Biomedical Applications of Monodisperse Magnetic Polymer Particles

The method developed by Ugelstad and coworkers1-3 for preparation of monosized polymer particles allows preparation of particles of any size from 1 to 100 µm with standard deviation in diameter ~ 1%. Also the method allows preparation of particles from a large number of monomers. Particles with highly crosslinked polymer of high mechanical strength, porous macroreticular particles and core and shell particles are prepared. The application of the porous macroreticular particles in fast protein liquid chromatography (FPLC)4 as marketed by Pharmacia is already well established and has in many cases led to very significant improvements in analysis and separation of complex protein mixtures.

Macroporous, monodisperse particles and their application in aqueous size exclusion chromatography of high molecular weight polysaccharides

Abstract Three different types of 15μm macroporous polymer particles (MP) based on poly(styrene- co -divinylbenzene), all with an extreme degree of monodispersity, were prepared by the method of ‘activated swelling’. The type and relative content of low molecular weight compounds used as pore-forming agents (porogens) ensured that the total pore volume was confined to large pores with radii larger than 300 A, and with an increasingly larger fraction of the pore volume shifted towards very large pores (> 2000A). A hydrophilic layer was covalently linked to the particles to eliminate their Hydrophobic character, and they were subsequently tested in aqueous size exclusion chromatography (SEC). Favourable Chromatographic properties generally associated with monosized particles were obtained, and column packing as well as the separations were performed with very low back pressures. The particles were found to be suitable for SEC of a series of high molecular weight polysaccharides, irrespective of their charge (anionic, cationic and neutral). The shift in pore size distribution towards very large pores resulted in a corresponding shift in the range of molecular weights (strictly, hydrodynamic volumes) where separation took place. For particles with 70% of the pore volume confined to pores with radii larger than 2000A, it was estimated that the molecular weight range of polysaccharides of the pullulan type accessible to SEC was extended up to ca. 10 8 . The corresponding value for an extended, rod-like, triple-helical polysaccharide (scleroglucan) was 10 7 .

Structure activity relationship of magnetic particles as MR contrast agents

Structure activity relationship (SAR) of superparamagnetic MR contrast agents is discussed based on physicochemical properties and relaxivity data of 16 different particles. All the magnetic particles reduce both relaxation times, T1 and T2. The effect on T2 is stronger than the effect on T1. The relaxation efficacy varies over a wide range. Minor modifications in the preparation of the magnetic particles result in products with different susceptibility properties. The T2 relaxivity is dependent upon the magnetic susceptibility as well as particle size. Small particles reduce the relaxation times to a larger extent than the larger particles. No significant difference in relaxivity is observed between compact and porous particles. Magnetic particles coated with nonmagnet polymer are effective relaxation agents, while nonmagnetic monodisperse particles show no effect on the relaxivity.