Packed capillary columns slurry packing

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. 

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. 

The influence of HPLC on the development of separation media for CEC is rather obvious. For example, HPLC-like hardware , such as frits and packed columns, are employed. A number of various packing technologies have been reported that enable packing particles into narrow bore capillary columns. The solvent slurry packing appears to be the most popular technique that has been transferred di-... 

Figure 8.1 Different types of microcolumns (a) open tubular capillary column (1-50 fim I.D.), (b) dry packed capillary column ( 200 jim I.D.), and (c) microbore column (0.5-1 mm I.D.), narrow-bore column (1-2 mm I.D.), and slurry packed capillary column ( 500 /xm I.D.). (Adapted from Ref. 2 with permission.)...

The most commonly used method to pack capillary columns for CEC utilizes the slurry packing methods typically used in HPLC. The capillary tube with a temporary frit is connected to a packing reservoir, such as a short HPLC column or another viable unit, which is connected to a high-pressure pump for solvent delivery. The slurry at a concentration of 50-100 mg/ml is prepared in a suitable solvent. Table 4.3... 

A different approach to MIP-based CEC involves immobilisation of MIP particles, of the same type as those that have been used for LC, inside capillaries [60-62]. The MIP was prepared in bulk from MAA and EDMA monomers in apolar porogens and subsequently crushed into small (<10 pm) irregular polymer particles. These particles were suspended in a solution of acrylamide/bis-acrylamide monomers and introduced into the capillary column where a poly(acrylamide) gel was formed [60]. A MIP particle slurry could also be contained within the capillary by closing each end of the capillary with a small plug of poly(acrylamide) gel (Fig. 16.2) [61,62]. The quality of the packing was not reported. An open, buffer-filled capillary with a detection window had to be connected to the MIP-filled capillary... 

Guide for slurry packing fused-silica capillary columns for capillary electrochromatography (i) Forming the bed-retaining frit... 

Hirata et al [5] achieved fairly high resolution of siloxane oligomers using a slurry-packed capillary column with 10% ethanol in n-hexane at 260°C. The chromatogram obtained is shown in Figure 9.18. The column consisted of a 50 cm X 0.2 mni I.D. length of fused silica packed with Finesil C18-10, and the mobile phase was programmed from 40-90 atm at 1.25 atm min... 

Li, W. Malik, A. Lee, M.L. Fused silica packed capillary columns using carbon dioxide slurries. J. Microcol. Separ. 1994, 6 (6), 557-563. 

Attaching an in-line end-frit and packing the column by pumping a slurry of beads and solvent into the capillary under high pressure. Sonication is recommended to achieve better quality. 

Colon and Maloney demonstrated another packing method that also avoids pumping the slurry through the column [51]. They used centripetal force to drive beads, which have a higher density than the liquid contained in solvent slurry, through the capillary. Their packing equipment enables a rotation speed of up to 3000 rpm at which the packing time is only 5-15 min. 

Several groups used sol-gel transition to immobilize the beads packed in a capillary. For example, Dulay et al. [102] packed a slurry of ODS beads in tetraethylorthosilicate solution and heated it to 100 °C to achieve the sol-gel transition and create the monolithic structure shown in Fig. 17. This technology is extremely sensitive and even a small deviation from the optimal conditions leads to cracks in the monoliths and a rapid deterioration in the column performance. However, even the best efficiency of 80,000 plates/m achieved with these column was relatively low. Henry et al. modified the original procedure and increased the efficiencies to well over 100,000 plates/m [103,104]. 

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