Packing material particle size distribution

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

FIGURE 1.3 15- m macroporous packing material, (a) Narrow particle-size distribution, (b) Close-... 

All packing materials produced at PSS are tested for all relevant properties. This includes physical tests (e.g., pressure stability, temperature stability, permeability, particle size distribution, porosity) as well as chromatographic tests using packed columns (plate count, resolution, peak symmetry, calibration curves). PSS uses inverse SEC methodology (26,27) to determine chromatographic-active sorbent properties such as surface area, pore volume, average pore size, and pore size distribution. Table 9.10 shows details on inverse SEC tests on PSS SDV sorbent as an example. Pig. 9.10 shows the dependence... 

Size, Particle Size Distribution, and Packed Density of Powdered Materials , MIL-STD-1233 (March 1962) 3) Anon, EngDesHdbk, Pro-... 

Powdered Teflon for use in pyrots is covered by US Mil Spec MIL-P-48296IPA) (1 May 1974), Polytetrafluoroethylene (TFE) . Three classes of material are specified (1,2 3). The requirements are purity, 99.4% min infrared spectrum, peaks consistent with figure shown color, TFE shall be opaque and the color shall range from white to gray moisture, 0.05% max ash, 0.1% max mp, 337° 10°C packing density, Class 1 — 1.18 0.13g/cc, Class 2 - 1.25 0.02g/cc, Class 3- 1.14 0.09g/cc particle size by sieve analysis, Class 1 — 95 15 microns, Class 2 — 237 27 microns, Class 3 — 200 30 microns particle size distribution by sieve analysis, as specified in Table 1... 

For L=NH3 (1) and L=Pr2NH (3), the isotherms are of type II as expected for non-porous materials [27]. Sample 2 shows a significant uptake at 0.6

narrow particle-size distribution which results in a more regular packing with interparticle pores of size similar to that of the particles [27]. The latter shows that the ligand-assisted synthesis does not only allow one to affect the total surface area and particle size, but also the size distribution which is an important tool for tailoring the particle properties. 

Chemical composition of packings. Today, a wider variety of different support materials is available from which to choose. Silica is still widely used, though preparative grades often possess a relatively wide particle size distribution as compared to polymer-based supports. One serious limitation of silica-based supports is the low stability of silicas to alkaline pH conditions, which limits use of caustic solutions in sanitization and depyrogenation. Polymer-based supports, which include poly(styrene-divi-nyl benzene)- or methacrylate-based materials, are widely available and have gained increased acceptance and use. Nonfunctionalized poly(styrene-divinyl... 

Wilson, T. D. and Simmons, D. M., A particle size distribution analysis of used HPLC column packing material, Chromatographia, 35, 295, 1993. 

MIL-STD-1233 - Procedure for Determining Particle Size Distribution and Packing Den-siry of Powdered Material MIL-STD-1235 — Single and Multilevel Continuous Sampling Procedures and Tests for Inspection by Attributes 2.2 Other Publications See Spec, pp 1 2 3. REQUIREMENTS... 

To give the particles the required momentum, they should be densely packed and rigid and have a well-defined narrow particle size distribution. Friable and oblique particles are not desirable because the penetration depth will increase if the particle characteristic is more variable (Hickey 2001). Studies have been performed with particles ranging from 20 to 40 J,m in size and 1.1 to 7.9 g/cm3 in density impacting human cadaver skin (Kendall et al. 2000). Velocities of up to 260 m/s were applied to particles of this size range. For many applications, smaller particles of about 1 to 4 j,m diameter may be required for an optimized delivery. To deliver particles of this size into the skin, higher densities and impact velocities are required. For this reason, gold particles are used as a carrier material for the delivery of plasmid DNA vaccines (Kendall et al. 2001). 

Particle chromatography using packed beds has attracted considerable attention of those interested in measuring particle size distribution of spherical particles in the submicron range (8,9, 1,14,16). There exist two complementary approaches to the use of this technique, according to the packing material employed ... 

The majority of CEC separations reported to date have been carried out on silica stationary phases that were originally developed for HPLC. Large differences have been observed [30] in using these HPLC phases in CEC. The differences seen in the separations of polycyclic aromatic hydrocarbon mixtures are far greater in CEC than would be expected for the corresponding HPLC separation. Two main reasons for this have been put forward (a) the differences in the packing of the capillary columns for CEC and (b) the particle size distribution of the materials, although all were nominally defined as 3 pm. 

The particle size distribution of packing materials has been shown to vary not only from one manufacturer to another but also with the measurement method used. For HPLC specifications, it is normal for manufacturers to give a particle size distribution based on an area distribution. However, this distribution has been pointed out [30] not to give a true distribution of the fine material... 

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