Capillary monoliths

FIGURE 7.13 Two-dimensional separation of tryptic digest of BSA in simple 2D-HPLC. Capillary monolithic silica-C18 column (0.1 mmi.d., 10 cm) was used as 2nd-D column. Mobile phase for 2nd-D gradient started with 0% B at 0.5 min, increased to 50% B at 3.3 min, to 100% B at 3.5 min, then returned to the initial condition and held for the last 0.5 min. Flow rate 3.0 pL/min in capillary, and 2 mL/min at the pump. Other conditions are similar to those for Figure 7.11 (reproduced from the reference, Kimura et al. (2004) with permission from Wiley). 

Recently an aromatic capillary monolithic acrylate material was prepared via a thermally initiated free radical polymerization in the confines of 200-pm inner diameter fused silica capillaries. The material proved to be very robust and was applied to IPC of oligodeoxynucleotides with good reproducibility [21]. Similarly a derivatized poly[(trimethylsilyl-4-methylstyrene)-co-bis(4-vinylbenzyl)dimethylsi-lane] capillary monolith was used for the same purpose [22],... 

Monolithic technology first originated as an alternate technique to fabricate capillary columns. It is a radical departure from packed-column technology and uses in situ polymerization to form a continuous bed of porous silica24 inside the fused silica capillaries. Because end frits are problematic in packed capillaries, this new approach eliminates this problem since no end frits are required for monoliths. For years, capillary monoliths remained a scientific tool for academic research. 

Finally, it is interesting to mention that capillary monolithic columns have also started to be used in gas adsorption chromatography [425, 426]. Poly-DVB monohth obtained in the presence of l.Svol of dodecanol-toluene mixtures possesses good separating power however, its efficiency (the theoretical plate height) still yields by a factor of 3-10 to that of traditional open capillary columns. On the other hand, the theoretical plate height for a similar monolith prepared for use in liquid chromatography proved to be comparable with that of conventional capillary silica-packed column [427]. 

With macroporous membranes, convective flow can be used as additional driving force for transport and separation (cf Section V.B). For separation s performance both binding aflinity and capacity will be important, especially when membrane adsorbers (cf Scheme 6b) shall be compared with other established or competing materials (beads, fibers, capillaries, monoliths). Again, membrane pore structure will have the main impact, because—if present—the micropore fraction will deter-... 

The macroporous monolith approach, introduced by Frechet and Svec, seemed to address many of the problems associated with open-tubular and particle packed columns. First, the adsorptive capacity of capillary monoliths has been found to be 3-5 orders of magnitude larger than that of both open channel and bead-packed columns [32]. Next, since the polymerization takes place within the fused-silica capillary, the tedious process of packing the capillary columns may be avoided. Furthermore, the limitations in chromatographic efficiency caused by irregularities in particle packing and by the nonuniformity of particle sizes are eliminated. 

The early attempts at fabricating molecularly imprinted capillary monoliths adapted the procedure set forth by Frechet and Svec [4] for the in situ preparation of non-MIP macroporous polymer rods for FC separation. In this procedure, porogenic solvents cyclohexanol and dodecanol (80 20 v/v) were used with a methacrylate-based polymer system to produce porous monoliths. When this system was applied to the fabrication of molecularly imprinted monoliths for CEC, the polymers obtained were sufficiently porous but resulted in poor enantiomeric separations [36]. It is thought that the polar-protic nature of the porogens used may have inhibited the formation of well-defined imprints. Polar-protic solvents such as these are often poor porogens for the noncovalent imprinting approach because they interfere... 

Natividad R, Ktdkami R, Nuithitikul K, Raymahasay S, Wood J, Winterbottom JM. Analysis of the performance of single capillary and multiple capillary (monolith) reactors for the multiphase Pd-catalyzed hydrogenation of 2-butyne-l,4-diol. Chemical Engineering Science 2004 59 5431-5438. 

H. Oberacher and C. G. Huber, Capillary monoliths for the analysis of nucleic acids by high-performance liquid chromatography-electrospray ionization mass spectrometry, Trends Anal Chem., 2002, 21(3), 166-174. 

Organic polymers are synthesized within capillaries, with polystyrene-divinylbenzene (PS-DVB) and polymeric methacrylates as the most common stationary phases. The most common process to make capillary monoliths includes opening silanol groups on the fused silica walls with sodium hydroxide, attaching a wall linkage, polymerization with monomer, cross-linker, porogen, and initiator, and sometimes grafting with other functionalities. 

E., Sellergren, B., Courtois, J., Irgum, K., Dambies, L., Cormack, P. A. G., Sherrington, D. C., Lorenzi, E. D., Chromatographic Comparison of Bupivacaine Imprinted Polymers Prepared in Crushed Monolith, Microsphere, Silica-Based Composite and Capillary Monolith Formats,/. 1160,215-226. 

L.S. Yan, Z.H. Wang, G. Luo and Y.M. Wang, Determination of caffeine by micro high performance liquid chromatography with a molecularly imprinted capillary monolithic column, Chinese J. Anal. Chem., 32 (2) 148-152, 2004. 

Figure 20 Analysis of human insulin in interstitial fluid samples using capillary monoliths of (a) 8 cm x 200 pm i.d. and (b) 8 cm x 50 pm i.d. Interstitial fluid samples diluted (a) 1 10 and (b) 1 160 and spiked with (1) human insulin (lOOfmolpM), injection volume 1 pi. Mobile phase ...

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