Stationary-phase particles, chromatography columns

Silica particles with grafted PNIPAM shell were used as a stationary phase for chromatography columns. The temperature sensitivity of PNIPAM can be used to tune the hydrophilic/hydrophobic balance in the chromatography column and to increase considerably the separation of steroids, peptides, and proteins. 

FIGURE 1.4 Optical micrograph of macroporous chromatographic column materials, (a) Monosized particles of 20 tm. (b) Commercial column filling of 12-28 tm. [Reprinted from T. Ellingsen et al. (1990). Monosized stationary phases for chromatography.7. Chromawgr. 535,147-161 with kind permission from Elsevier Science-NL, Amsterdam, The Netherlands.]... 

In exclusion chromatography, the total volume of mobile phase in the column is the sum of the volume external to the stationary phase particles (the void volume, V0) and the volume within the pores of the particles (the interstitial volume, Vj). Large molecules that are excluded from the pores must have a retention volume VQ, small molecules that can completely permeate the porous network will have a retention volume of (Vo + Fj). Molecules of intermediate size that can enter some, but not all of the pore space will have a retention volume between VQ and (V0 + Fj). Provided that exclusion is the only separation mechanism (ie no adsorption, partition or ion-exchange), the entire sample must elute between these two volume limits. 

Size exclusion chromatography. The separation occurs because the stationary phase particles are porous and the small molecules enter the pores and are slowed from passing through the column, while the large molecules pass through more quickly since they do not enter the pores. 

Chromatography column packed with stationary phase particles... 

The term A is related to the flow profile of the mobile phase as it traverses the stationary phase. The size of the stationary phase particles, their dimensional distribution, and the uniformity of the packing are responsible for a preferential path and add mainly to the improper exchange of solute between the two phases. This phenomenon is the result of Eddy diffusion or turbulent diffusion, considered to be non-important in liquid chromatography or absent by definition in capillary columns, and WCOT (wall coated open tubular) in gas phase chromatography (Golay s equation without term A, cf. 2.5). 

Figure 23-19 Band spreading from multiple flow paths. The smaller the stationary phase particles, the less serious this problem is. This process is absent in an open tubular column. [Adapted from H m. McNair and E. J. Bonelli, Basic Gas Chromatography (Palo Alto. CA Varlan Instrument Division. 1968).]...

The use of hydrothermally formed retaining frits in capillary columns packed with stationary phase particles is an accepted limitation in CEC. The introduction of the frit to hold the packed bed is vital, yet introduces problems such as EOF and flow non-uniformities, compromised frit permeability [87], capillary fragility, increased likelihood of bubble formation [88] and a thermally induced modified frit surface chemistry which can detrimentally alter the chromatography [23]. Practical aspects to be considered include the appreciable effort and skill of the analyst who is required to repeatably manufacture capillaries of a particular phase and redevelop the fritting and packing methodology for each different stationary phase type. 

Capillary column gas chromatography gas chromatography using columns 10-100 m long with an internal diameter of 0.1-0.7 mm, usually with the stationary phase bonded to the internal wall (WCOT). Capillary columns have high efficiencies ( eir) and give rapid analysis times. The A term in the van Deemter equation is zero as the column does not contain stationary phase particles or packing. 

Now consider the maximum achievable column efficiency as measured by the number of theoretical plates N pj. For this purpose help is obtained from the water engineers An important relationship used to evaluate flow rates of water through porous media is d Arcy s Law (see http //biosystems.okstate.edu/darcy/). The principles underlying d Arcy s original formulation also apply to liquids other than water and the law can be expressed as follows in a form appropriate to flow of a mobile phase through a bed of stationary phase particles (Scott http //www.chromatography-online.org/) ... 

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