Packings pellicular

The large particle size allows H to be further approximated to 

A major disadvantage of pellicular packings is the low surface area associated with the shallow pores which limits sample capacity. 

---

Unlike the pellicular packings used for ion exchange, the packings used in ion exclusion are derived from totally sulphonated polymeric materials. Separation is dependent upon three different mechanisms Donnan exclusion, steric exclusion and adsorption/partitioning. 

The dimensions of the packing material are important in achieving efficient separations and the flow pattern around particles causes mixing of solute and solvent and increases the dilution effects, contributing to the phenomenon known as band broadening (Figure 3.9). Pellicular packing materials are... 

For reasons explained in Section 19.5.3, large-scale LC employs larger particles (10-70 xm) than analytical HPLC. This increases the Cmu term by deepening the intraparticle pores containing stagnant mobile phase to be penetrated by the solute. (See note to Table 19.1). Pellicular packings, in which each particle contains only a superficially porous layer with an inner solid core, have been used, though the present trend is towards totally porous particles of 15-25 p,m. 

A breakthrough in ion chromatography came from pellicular packings, which were introduced by Dionex. Packing consists of an inert, nonporous, chemically and mechanically stable core, a surface sulfonated area covering the core, and an outer layer of permanently attached submicron ion exchange. 

Pellicular Packing—First analytical packing it had a solid core and a crust of porous silica. Now used primarily for packing guard columns and columns for separating very large molecular weight compounds (i.e., DNA, RNA). 

To protect the column from compounds that irreversibly adhere to or partition into the column packing, a precolumn may be used. A pellicular packing coated with C g material (Cjg Corasil II, Waters Associates) has proven beneficial, yet has a minimally detrimental effect on compound resolution. 

I Pellicular packing. A solid core surrounded by a thin porous crust of smaller particles. These particles are an economical means of obtaining moderately high efficiencies for analytical work. Also, they are popular as pack-) ings in guard columns to protect analytical columns. ... 

Guard columns may be filled either with pellicular material (see Fig. 3-13) of the same bonded phase as the analytical column or with the identical packing material as in the analytical column. Pellicular packings (35-40 /urn)... 

Pellicular packings may also consist of a fully functionalized layer encapsulating solid particles, where there is no physical attachment of the active layer to the core particles [7] or as colloidal particles bearing charged moieties (latex) electrostatically bound to a solid core functionalized with groups of opposite charge [8] (Fig. 1). Most of the anion-exchange columns in use today for either carbohydrate or ion chro-... 

It is obvious that the cleaner the sample, the longer the column life. On the other hand extensive clean-up procedures are time consuming. A compromise can be the use of precolumns to protect the analytical column against contamination caused by impurities present in the sample. Precolumns can be prepared from less expensive material than the analytical columns, i.e. pellicular packings or large diameter particles, which can be easily dry-packed. However, microparticulate stationary phases have also been used. As HPLC analysis of alkaloids often deals with the determination of low concentrations of alkaloids in a complex matrix, some factors concerning the sample preparation which influence the detection limit are worth consideration. 

Most LC stationary phases are now either bare of surface derivatized micro-sporous silica particles of 10, 5, or 3 pm in diameter. These small-diameter packings provide very high efficiencies due to rapid mass transfer, in contrast to the much larger pellicular packings of the 1970s. In a survey of column usage taken in 1994, 24.6% of respondents reported using 1-3 pm materials 71.3% reported... 

---