Flow asymmetry factors

Elution volume, exclusion chromatography Flow rate, column Gas/liquid volume ratio Inner column volume Interstitial (outer) volume Kovats retention indices Matrix volume Net retention volume Obstruction factor Packing uniformity factor Particle diameter Partition coefficient Partition ratio Peak asymmetry factor Peak resolution Plate height Plate number Porosity, column Pressure, column inlet Presure, column outlet Pressure drop... 

Fig. 6-7. Asymmetry factor (AJ of the L-enantiomer versus sample load (A) and versus flow rate (B) on L-PA-imprinted polymers. Flow rate 1.0 ml min . Mobile phase MeCN/[potassium phosphate 0.05 M, pH 7] (7/3, v/v).

Having chosen the test mixture and mobile diase composition, the chromatogram is run, usually at a fairly fast chart speed to reduce errors associated with the measurement of peak widths, etc.. Figure 4.10. The parameters calculated from the chromatogram are the retention volume and capacity factor of each component, the plate count for the unretained peak and at least one of the retained peaks, the peak asymmetry factor for each component, and the separation factor for at least one pair of solutes. The pressure drop for the column at the optimum test flow rate should also be noted. This data is then used to determine two types of performance criteria. These are kinetic parameters, which indicate how well the column is physically packed, and thermodynamic parameters, which indicate whether the column packing material meets the manufacturer s specifications. Examples of such thermodynamic parameters are whether the percentage oi bonded... 

In pHPLC, there are numerous types of columns used. The comparison and characterization of these columns are often discussed in terms of thermodynamic properties and kinetic characteristics. The retention factor, k, selectivity, a, and the peak asymmetry are believed to be representative parameters for the thermodynamic properties, while the kinetic characteristics are often expressed in dimensionless magnitudes of reduced plate height, h, separation impedance, E, and flow resistance factor, ( ). 3... 

The same SEC flow system (Figure 1) and mobile phase as described in the previous section were used in the size measurement. The mobile phase flow rate was 0.6 cm /min and the sample size was 50 yl. The precision of the flow rate was better than 0.4% (at 95% C. I.). The three-column set had a total retention volume of 33.6 0.1 cm. The amount of column dispersion of the column set was estimated from the peak contour of a potassium nitrate solution slug. Using the moment method described by Grushka the band-broadening and peak asymmetry factors were determined to be 0.56 and 0.27 cm respectively. 

BEDROCK CHARACTER Is local bedrock an important factor in local hydrologic system If so, do textures or structures in bedrock produce asymmetry or enhanced flow of potential leachate plume (flow along bedding, joints, faults, or solution channels). 

An important factor leading to asymmetry is the variations in the cross-sectional area among channels. A main cause for this is the GDL intrusion into the channel space. Figure 31.19a presents the velocity contours in flow channels with 20% area maldistribution, which shows the flow maldistribution clearly. The standard deviation of the normalized flow through the channels is 0.315 [46]. 

Equation (4.10) applies only to symmetrical peaks. Asymmetrical peaks show that infinite dilution has not been attained and the more general eqn (4.8) should be used. The asymmetry originating in kinetic factors or those not depending on the column may not be api)lied in any theory and therefore it should be avoided, for instance by utilizing low flow rates. In the following is assumed that the asymmetry of peaks is not due to these factors. 

Factors that affect erosion in pipe bends include the degree of internal eUipticity and asymmetry discussed earlier, sudden chsinges in cross section, and reduction in cross-sectional area [5/]. As the radii of directional change are reduced, the erosion corrosion rate is expected to increase. Ledges, crevices, deposits, and other obstructions disturb laminar flow and result in turbulence at significant velocities [40]. Short distances less than 10 diameters after directional changes or obstructions do not allow turbulence to dissipate [52]. 

It is interesting to note that the result in Eq. (4) is the same as the result for a rigid, massless sphere in Stokes flow except for a factor 1/2. Moore [11] extended the above result to include finite Reynolds number effects. Moore [12] also developed a result for a spheroidal bubble. El Sawi [13] extended Moore s theory to include the effects of fore-aft asymmetry. 

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