Specific column permeability

The velocity we can obtain at a given pressure will also be limited by the resistance to flow presented by the column, known as the specific column permeability. In equation (17-16) the permeability is broken up into its two main components the flow resistance parameter, ( ), and the particle diameter squared, dl, and can be expressed as... 

Column gas velocity is dependent upon the column length, carrier gas viscosity, pressure drop through the column and the column permeability. Column permeability is expressed by the specific permeability coefficient, B0, which may be calculated by the following expression. 

Measurement of column permeability is not clear-cut. The permeability of a column can be determined in several different ways. For example, it can be measured as the specific permeability, K° (EQ. 3), which corrects for mobile phase viscosity and column length (5) ... 

Usually tailed peaks were obtained. Formic acid, water cind carbon disulfide act as effective peaktailing reducers [8]. In the authors opinion [8], sandwiched capillary columns may be regarded as a set of equal micro-capillaries and specific gas permeability and other operational chromatographic parameters of sandwiched columns compare favorably with those of packed capilleiry columns. Fig. 6-28 [8] shows chromatograms of geometric isomers on WYB sandwiched columns. The results are promising. 

Table 7.23 shows the results for 47 specific PAMPA models tested at pION, according the the scheme in Fig. 7.58. The two columns on the right are the r2 values in the comparisons. The neutral-lipid models (1.0, 1A.0, 2.0, 3.0, and 4.0) at pH 7.4 do not explain the permeability trend indicated in the human jejunal permeabilities [56]. Octanol was least effective, with r2 0.01. This should not be too surprising, since we did note that the appearance of naproxen, ketoprofen, and piroxicam at the top of the HJP ordering was unexpected. Our expectations were based on the octanol-water lipophilicity scale, which clearly does not correlate with the HJP trend. Adding a sink condition to the 2% DOPC model (model 1.1) improves correlation (r1 increases from 0.33 to 0.53). The addition of cholesterol to the 2% DOPC/dodecane system made the model unstable to the surfactant-created sink condition. 

High performance monolithic columns were prepared from styrene and divinyl-benzene (PSDVB, 200 pm i.d.) (Oberacher et al., 2004). The monoliths possess 5-300 nm pores with porosity of ca. 50% and 20% for external and internal pores, respectively, with specific surface areas of 30-40 m2/g. The column showed permeability K= 3.5 x 10 15m2 in water and slightly less in acetonitrile. The pore size... 

Equation 6 Calculation of optimum ratio of particle size and column length, with selectivity factor, a capacity factor of second component of critical pair under analytical chromatography conditions, fe 02 diffusion coefficient, (cm /s) (typical value for MW 1000 10 cm /s) viscosity, p (cP) specific permeability (1.2 X 10 for spherical particles), feo third term of the Knox equation, C and maximum safe operating pressure, Ap, (bar). 

Since chromatographic flow is laminar in nature, the specific permeability (Bq) of a packed column can be calculated using the Darcy equation [131,132]... 

The solution of Eq. 1 requires specification of boundary conditions (BCs) and additional equation(s) that describe the sorption reaction. The assumptions reflected in these choices strongly influence the process of extrapolating barrier performance from laboratory column data. Furthermore, as discussed below, there are significant differences in the treatment of these choices between low- and high-permeability systems. 

Because diffusion dominates the transport of contaminants in barriers and columns constructed of low-permeability materials, model calibrations and predictions are extremely sensitive to the form of the specified boundary conditions. Two issues are of particular importance 1) treatment of the entrance mixing zone in laboratory columns, and 2) specification of appropriate BCs to represent a slurry wall under field conditions. 

A liquid chromatographic column packed with 5.00 fim diameter solid support particles and having a porosity e = 0.400 is found to have a flow resistance parameter 750. Calculate the specific permeability K0. Assume that the flowrate/pressure drop relationship is identical to that of a bundle of identical parallel capillaries whose axes are spaced (in a square cross-sectional array) a distance of 5.00 /im from one another. What is the single capillary diameter of the hypothetical bundle ... 

Together with u, and Ap, the specific permeability, K°, is also linked with the solvent viscosity, p, and the column packing porosity, s. ... 

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