Packings microparticles

New types of ion exchange resins have also been developed to meet the specific needs of high-performance liquid chromatography (HPLC) (Chapter 8). These include pellicular resins and microparticle packings (e.g. the Aminex-type resins produced by Bio-Rad). A review of the care, use and application of the various ion exchange packings available for HPLC is given in Ref. 19. 

OUTLINE OF SLURRY PACKING TECHNIQUES FOR RIGID MICROPARTICLES... 

We have found that ethanol works well for this purpose. When microparticle-packed HPLC columns are used, the solvent change must be accomplished as a gradual, continuous gradient. Discontinuous increments (step gradients) tend to cause rapid viscosity and thermal changes along the column bed these are known to cause destruction of the bed. 

The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm x 25-cm column containing packing LI (octadecyl silane chemically bonded to porous silica or ceramic 3-10 pm microparticles). The flow rate is about 2 mL/min, and the column temperature is maintained at 40°C. 

Porous microparticles are the most common stationary phase particles used in modern HPLC. The role of pore size is a critical one, as the pores provide the surface with which the sample interacts. Particles with small pores exhibit a high surface area and therefore have greater retention. Large molecules like proteins, however, may be excluded from the small pores, and for those molecules a packing with a larger pore size is preferable. The difference between porous particles, pellicular particles, and porous microparticles is illustrated in Figure 3.19. Porous particles are seldom used owing to low efficiencies and are not discussed further. 

Procedure (See Chromatography, Appendix IIA.) Use a high-performance liquid chromatograph equipped with an ultraviolet detector that measures absorption at 254 nm and a 25- to 30-cm x 4-mm (id) stainless-steel column, or equivalent, packed with octadecyl silane chemically bonded to porous silica or ceramic microparticles 5 to 10 pun in diameter, or equivalent. Maintain the mobile phase at a pressure and flow rate capable of giving the required resolution (see below). Inject a volume, up to 25 pL, of the System Suitability Solution in a similar manner. Calculate the resolution, R (>3.6), between calcium formyltetrahydrofolate and Folic Acid by the equation... 

RPLC was coined). Later, Majors [5] introduced porous silica microparticles modified with alkylsilanes, a packing material that is almost exclusively used in reversed-phase HPLC today. 

When used mainly as a contacting device, the membrane material leads to considerably improved performance for transfer and/or reaction as compared to a classical packing. This is due to a better management of fluid dynamics and mixing conditions, to increased surface areas and to better controlled driving forces. In fact the membrane represents the assembly of a multitude of microsystems, which act in parallel and can be functionalized. With materials structured at the nanoscale level it would be possible to control phenomena at the molecular level. As compared to dispersed beds of microparticles, porous layers have the main advantage of keeping... 

Narrow-Bore Microparticle-Packed Column High Performance Liquid Chromatography... 

The driving forces for the rapid development and growth In mlcrobore column HPLC are (1) savings In solvent consumption a total saving of up to 99.9% can be achieved when narrow-bore microparticle packed columns or open—tubular micro-capillary columns are used (2) the high separation power using long column and small particles (e.g., 3 nm) (3) the compatibility of the column eluent flow rates with a mass spectrometer and flame based detectors and (4) opportunities In new detector development,... 

In addition to the high separation efficiency and resolving power of the fused-slllca narrow-bore microparticle packed columns, several other practical advantages are cited below ... 

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