Columns, capillary particle-packed

Figure 2 Frontal zone profile of electroosmotic flow in packed capillary column. The capillary column was packed with silica gel (particle diameter 5 pm). The medium was cyclohexanol. As cyclohexanol and silica gel have similar refractive indexes, the column looked transparent. The lower photo was taken 31 s after the upper one.

This parameter relates the particle size, flow velocity, column length and mobile phase viscosity to the pressure drop required to achieve aU of these characteristics (an important parameter for practical operation of capillary columns). For packed columns a useful range for ] is 500-1000 (Knox 1980). For a series of columns that differed in de between 20 and 50p,m it was found (Kennedy 1989) that (]) ranged between 600-800 with a slight decrease for lower i.d. columns. 

Equation (11) accurately describes longitudinal diffusion in a capillary column where there is no impediment to the flow from particles of packing. In a packed column, however, the mobile phase swirls around the particles. This tends to increase the effective diffusivity of the solute. Van Deemter introduced a constant (y) to account... 

The development of the function describing (tm) for a capillary column is similar to that for the packed column but (r), the column radius, replaces (dp), the particle diameter. 

Five types of columns are routinely used in gas chromatography classical packed columns with internal diameters greater than 2 mm containing particles in the range 100 to 250 micrometers micropacked columns having diameters less than 1 mm with a packing density similar to classical packed columns (dp/d less than 0.3, where dp is the particle diameter and d the column diameter) packed capillary lumns have a column diameter less than 0.5 mm and a packing density less than classical packed columns (dp/d 0.2-0.3) SCOT columns (support-coated open... 

Slurry packing techniques are required for the preparation of efficient columns with rigid particles of less than 20 micrometers in diameter. The same general packing apparatus. Figure 4.8, can be used to pack columns by the balanced-density slurry, liquid slurry, or the viscous slurry techniques. Down-fill slurry packing is the method of choice for small bore columns and packed capillary columns. 

Chromatography by ion exchange on a sulfonated poly(styrene-co-divinyl benzene) phase has been proposed as a replacement for titrimetry.57 Eluted by a dilute solution of a neutral salt such as sodium ethanesulfonate, the conductance of the protons can be measured in the absence of a suppressor from sub-millimolar to molar concentration. The response factors of mono-, di-, and trichloroacetic acid and of o-phthalic acid were large and essentially equivalent to ethanesulfonic acid, while the response factor of acetic acid was far smaller. A syringe pump has generated pressures as high as 72,000 psi (5000 bar) in a capillary column packed with 1 p particles, generating a fraction capacity of 300 peaks in 30 minutes.58... 

The main interest in cSFC comes from the high efficiency that can be obtained for involatile samples. The capillary column has the advantage of being able to chromatograph many analytes without additional solvent modifiers. cSFC generates two to three orders of magnitude more theoretical plates for a given separation than a typical packed column of 5 xm particles. 

SFE can be combined with several forms of SFC, i.e. with conventional packed columns (l-4.6mm i.d. packed-column SFC or pSFC), with capillary columns (10-250 xm i.d. capillary SFC or cSFC), and recently with packed capillary columns (200-530 p,m i.d., 3-10 xm particles packed capillary SFC or pc-SFC). 

Chromatographic use of monolithic silica columns has been attracting considerable attention because they can potentially provide higher overall performance than particle-packed columns based on the variable external porosity and through-pore size/skeleton size ratios. These subjects have been recently reviewed with particular interests in fundamental properties, applications, or chemical modifications (Tanaka et al., 2001 Siouffi, 2003 Cabrera, 2004 Eeltink et al., 2004 Rieux et al., 2005). Commercially available monolithic silica columns at this time include conventional size columns (4.6 mm i.d., 1-10 cm), capillary columns (50-200 pm i.d., 15-30 cm), and preparative scale columns (25 mm i.d., 10 cm). 

Correlation was found between domain size and attainable column efficiency. Column efficiency increases with the decrease in domain size, just like the efficiency of a particle-packed column is determined by particle size. Chromolith columns having ca. 2 pm through-pores and ca. 1pm skeletons show H= 10 (N= 10,000 for 10 cm column) at around optimum linear velocity of 1 mm/s, whereas a 15-cm column packed with 5 pm particles commonly shows 10,GOO-15,000 theoretical plates (7 = 10—15) (Ikegami et al., 2004). The pressure drop of a Chromolith column is typically half of the column packed with 5 pm particles. The performance of a Chromolith column was described to be similar to 7-15 pm particles in terms of pressure drop and to 3.5 1 pm particles in terms of column efficiency (Leinweber and Tallarek, 2003 Miyabe et al., 2003). Figure 7.4 shows the pressure drop and column efficiency of monolithic silica columns. A short column produces 500 (1cm column) to 2500 plates (5 cm) at high linear velocity of 10 mm/s. Small columns, especially capillary type, are sensitive to extra-column band... 

Patel, K.D., Jerkovich, A.D., Link, J.C., Jorgenson, J.W. (2004). In-depth characterization of slurry packed capillary columns with l.O-pm nonporous particles using reversed-phase isocratic ultrahigh-pressure liquid chromatography. Anal. Chem. 76, 5777-5786. 

FIGURE 14.3 Fast analysis of control drugs and metabolites using a 15 cm x 300 fim inner diameter capillary column packed with 3 /tin C18 particles (Micro-Tech Scientific MC-15-C18SS-320-EU) operated at 10 /tL/min gradient flow rate. UV at 278 nm. (Source Drug Enforcement Administration, Southwest Laboratory, Vista, California and S. DiPari.)... 

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