Micropellicular particles

Pellicular or controlled surface porosity particles were introduced in the late 1960s these have a solid inert impervious spherical core with a thin outer layer of interactive stationary phase, 1-2 pm thick [13]. Originally, the inner sphere was a glass bead, 35-50 pm i.d., with a thin active polymer film or a layer of sintered modified silica particles on its surface. Such particles were not very stable, had very low sample load capacities because of low surface areas and are not used any more. Nowadays, this type of material is available as micropellicular silica or polymer-based particles of size 1.5 to 2.5 pm [14]. Micropellicular particles are usually packed in short columns and because of fast mass-transfer kinetics have outstanding efficiency for the separation of macromolecules. Because the solutes are eluted as very sharp narrow peaks, such columns require a chromatograph designed to minimise the extra-column contributions to band broadening. 

Columns packed with pellicular stationary phases of small particle size have low permeability and, therefore, cannot be operated at relatively high flow rates due to the pressure limitation of commercial HPLC instruments. However, due to the non-porous structure, micropellicular particles are generally more stable at higher temperature than conventional porous materials. Consequently, in the... 

Purification of double-stranded DNA on micropellicular anion exchange and reversed-phase materials has been reviewed.43 Micropellicular phases adsorb only at the surface and have no internal pores. For this reason, the surface area and hence the capacity of micropellicular phases tends to be low. Using small particles (1-3 p in diameter) increases the surface area but may be impractical for preparative work above the mg scale. 

The need for enhanced detection sensitivity and automation has steadily increased for the separation and analysis of peptides from natural sources or proteolytic digestion of low abundance proteins this is also partly a consequence of the greater usage of combinatorial solid-phase synthetic approaches. Narrow bore (1-2 mm i.d.), microbore (0.5-1.0 mm i.d.), and capillary (100-500 pm i.d.) columns have provided attractive solutions to these problems. 1221 An important attribute of very small particle diameter micropellicular, porous, or nonporous RPC sorbents is that they are ideally suited to such microbore or capillary... 

Due to small particle size, the columns packed with micropellicular stationary phases have low permeability (27) and therefore, can not be operated at very high flow rates due to pressure limitations of commercial HPLC instruments. In comparison to porous particles, the surface area of stationary phases per unit column volume is low, and hence, their loading capacity is correspondingly smaller. This is particularly evident in the isocratic analysis of small molecules where the column can be easily overloaded. Therefore, micropellicular sorbents do not appear to offer advantages in the HPLC of small molecules. 

An important advance in the RP-HPLC impurity analysis of proteins has been the advent of short columns containing micropellicular stationary phases.42 These short columns contain nonporous particles of the order of 2 pm that are capable of attaining high flow rates ( 4 mL/min) at elevated temperatures ( 80° C). Such a configuration leads to very rapid and highly... 

A very simple way to achieve a reduction in the intraparticular mass transfer is the use of micropellicular, i.e., nonporous particles. However, due to the low capacity of such particles (90% of the adsorptive surface is usually found inside a particle), such nonporous particles are more suitable for analytical than for preparative applications. Another way to increase capacity without relying on the intraparticular surface area, which is more suitable to preparative applications, is represented by the so-called tentacle gels. Gigaporous stationary ( perfusion ) particles and hyperdiffusive ( gel in a shell ) particles can also be envisaged for preparative separations. 

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