Nonporous packing material

If Ig of conventional porous packing material has an average of 300m /g surface area, the same 1 g of nonporous packing material with particle diameter of just 1 pm has only 2.7 m /g or about 100 times lower surface area. This means that these columns require approximately 100 times lower injection volume and higher detector sensitivity. 

The simplest way to eliminate the problems of porous particles is to eliminate the pores. Nonporous particles of 10 pm diameter with a thin layer of stationary phase on their surfaces were in fact introduced early in the evolution of HPLC packings as a solution to the pore problem, but achieved little popularity because of their low capacity. Recently, nonporous materials have returned to the marketplace in the form of very small particles with diameters of 1.5 to 2.5 pm. The use of small particles compensates to some extent for the loss in capacity.11 However, because of the high flow resistance of microparticulate nonporous packings, they are generally packed in short lengths and often operated at elevated temperatures. 

The use of column with superficially porous packing materials based on silica particles with nonporous cores is the most recently reported strategy for improving chromatographic performance. This technology, originally developed by Kirkland in the 1990s to limit diffusion of macromolecules into the pores [85], became commercially available in 2007 [86], In comparison with totally porous particles of similar diameters, the both A and C term of the Van Deemter curve are reduced [87, 88],... 

TYPE OF PACKING MATERIAL (POROUS, NONPOROUS, MONOLITHIC)... 

HPLC columns contain, usually, spherical particle packings, which are carefully sorted to fractions with narrow size distribution to provide high separation efficiency. Totally porous packing materials most frequently used for separations of small molecules in contemporary HPLC have pore sizes of 7-12 nm and specific surface area of 150-400 m /g, but wide-pore particles with pore sizes of 15-100 nm and relatively low specific surface area of 10-150 m /g, or nonporous materials are used for separations of macromolecules. Perfusion materials, designed especially for the separation and isolation of biopolymers, contain very broad pores (400-800 nm) throughout the whole particle, which are interconnected by smaller pores. Column efficiency and flow resistance increase with small particles, and a high pressure has to be used to maintain required flow rate and to keep an acceptable time of analysis. However, the maximum operating pressure is 30-40 MPa, with common instrumentation for HPLC. Hence, short columns should... 

Except for nonporous particles, all packing materials contain a variation of pore sizes around a mean value. This pore size distribution determines the range of... 

Where impurities are present as microparticulate material filtration affords a convenient technique for solvent purification. The mobile phase containing added buffers or reagents may be filtered through a 0.5 pm or smaller filter to remove particulate matter that can damage the analytical system. The equipment for filtration is simple. Usually, it consists of an Elenmayer flask connected to vacuum and a reservoir in which a porous filter disk or membrane is placed. The porous disk is usually made from nonporous spherical glass beads (1-2 pm) and/or polytetrafluoroethylene (PTEE). Membrane materials are usually made from PTEE, cellulose, or nylon. To improve the efficiency of the separation process, the surface of the filter disks or membrane surface are often modified chemically, similar to that used for chemically bonded packing materials in RP-HPLC and/or SPE. In this case, the surface properties (hydrophobic or hydrophilic) of filters and/or membranes determine the extent of purification possible. 

Nonporous packings with very small particle diameters have developed into useful tools for fast and economic separations. Due to the reduced resistance to mass transfer of the nonporous material, separation efficiency is increased at high flow... 

Packing materials for the HPLC separation of biomolecules that have not only 500-1500 A pores but also a network of 6000-8000 A transecting tunnels have been developed by Regnier. These highly porous materials, when packed into columns, permit mobile phase velocities 2-5 times higher than those for conventional wide pore silica columns. For the rapid reversed-phase separation of peptides and proteins, both small 2-yrm porous wide pore (200 A) silica and l-jxm pellicular silica microspheres packed in 3-cm columns have been developed. For a five component mixture of proteins, separation times of less than a minute were possible. Nonporous monodisperse 1.5-yj.m silica beads developed by Unger have been shown... 

When a penetrating colored dye solution is injected into a package it detects channels or voids in the sealed area via capillary action and pinholes in nonporous materials via blotting on a paper tissue. Packs with at least one transparent component are more suitable for viewing the results. Dye penetration is more difficult to use on packages of porous materials, such as paper. 

The column length varies from 3 to 30 cm, the inner diameter from 1 to 10 mm. Columns are made of very resistant materials to withstand high pressures (<40 MPa) Most commonly, a stainless steel or heavy-walled glass tube is inserted into a metal tube. Columns are packed with a solid material of particle size <10 pm (spherical and nonporous microglass beads or polymer particles). A guard column is usually placed before the column to remove suspended particles from solvents, as well as certain sample constituents that could irreversibly bind to the stationary phase. 

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