Packing length

The column. The actual separation of sample components is effected in the column where the nature of the solid support, type and amount of liquid phase, method of packing, length and temperature are important factors in obtaining the desired resolution. 

FIGURE IS Electrochromatograms obtained for the separation of basic drugs spiked in a human serum compared with a blank in a hydrophobic interaction CEC. Column 5 pm 300 A polysulfoethyl A particles, 20 cm packed length, 50 pm ID mobile phase ACN/TEAP buffer (80 20) applied voltage, 10 kV detection at 214 nm. Drugs (I) amobarbital (2) phenobarbital (3) barbital (4) caffeine (5) sulfanilamide (6) theophylline (7) 2,4-dimethylquinoline (8) propranolol. (Reproduced with permission from reference 76.)... 

Once a open and <3packed are known, the potential drops across the two segments of either column with packed length, Lpacked, are evaluated by using the following expressions [18,20]... 

Fig. 1.2. Plots of the potential drop across the packed and the open segment of a CEC column against the dimensionless packed length, X, with conductivity ratio, aoperXvpacked, as the parameter. The respective currents with columns having packed segments of 0, 10 and 20 cm were reported as 6.6, 3.9 and 2.6 p.A, respectively. The conditions were fused silica capillary, 50 pm x 30 cm applied voltage, 18 kV column packing, 3.5 mm Zorbax ODS, 80 A mobile phase, 50 % (v/v) ACN in 10 mM sodium borate, pH 8.0.

The final expression for the flow equalizing intersegmental pressure Pi as given by Eq. 1.42 can be rewritten in terms of the dimensionless packed length, X, as follows... 

The pressure difference, Pi - Po, as calculated from Eq. 1.43 is plotted as a function of the dimensionless packed length, X, with the conductivity ratio as the parameter in Figure 1.9. The pressure drop across any of the segments, Pi - Po, is maximum at small X values and becomes zero at the extremity X = 1. In the present... 

Figure 1.12 illustrates that the design of the CEC column in terms of the dimensionless packed length, X, has a profound influence on the separation when the sample contains both neutral and charged components. It is seen that satisfactory separation of all five components can be achieved with CEC columns having X values in the range 0.2-0.6. Nonetheless, the speed of separation has also to be considered in most cases. The separation is almost two times faster when X is about 0.2 than when X = 0.6. Thus in the case illustrated, a CEC column with a packed length of 20 % can provide a rapid and efficient separation of components A, B, C, D and E. 

Fig. 10.19. Electrochromatogram of protein separation on a diol. Conditions pH 4.14, capillary 450 mm x 50 pm i.d., 250 mm packed length. Peak identification 1, cytochrome c 2, lysozyme 3, myoglobin 4, ribonuclease A. Reproduced with permission from Pesek et al. [102].

Polyaromatic hydrocarbons (benzene, toluene, naphthalene, acenaphthylene, fluor-ene, anthracene, 1,2-benzanthracene, phenol, acetone) ODS Hypersil, 5 pm Gradient acetonitrile-water (from 60 40 to 90 10) 500 mm x 75 pm i.d. 200 mm packed length, flow-injection analysis... 

Polyaromatic hydrocarbons and parabenes (ethyl-hexyl parabene, naphthalene, fluo-rene, phenanthrene, fluoranthene, pentylbenzene) Excil C18 Acetonitrile-Tris HC1 buffer pH 8.0 (80 20) 380 mm x 100 pm i.d. 85 mm packed length... 

Malto-oligosaccharides Custom made macroporous polyacrylamide-poly(ethylene glycol) matrix 10 mMTris + 15 mMboric acid (pH 8.2) in acetonitrile-0.1% acetic acid (5 95) 320-500 pm i.d. 250-400 mm packed length 36... 

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