Microfabricated columns

Figure 2.16 Representation of (a) layout of a typical COMOSS separation column and (b) an SEM image showing the microfabricated inlet splitter [115].

He, B., Regnier, F., Microfabricated liquid chromatography columns based on collocated monolith support structures. J. Pharm. Biomed. Anal. 1998, 17, 925-932. 

Vervoort, N., Billen, J., GzQ, P., Baron, G.V., Desmet, G., Importance and reduction of the sidewall-induced band-broadening effect in pressure-driven microfabricated columns. Anal. Chem. 2004, 76, 4501-4507. 

Also, EOF velocity in plastic microchannels had been imaged using video imaging of caged fluorescent dye [92], Dispersion of the uncaged dye for microchannels composed of poly-(dimethylsiloxane) (PDMS) was similar to that found in fused silica capillaries. The calculated EOF mobilities in different mobile-phase systems for various channels (acrylic, PDMS, acrylic/PDMS hybrid) were similar. This work shows that EOF profile is similar in microfabricated devices and in capillary columns. 

An integrated microfabricated system composed of a proteolytic reactor and chromatographic column with direct interface to ESl-MS was reported by Carlier et al. [133] The system is represented in Fig. 11 and was fabricated from SU-8. The chromatographic end of the chip was terminated with a nano-ESl interface. The digestion module was composed of trypsin covalently attached to a monolithic polymer, which was also used to prepare a hydrophobic stationary phase for the separation of peptides prior to MS analysis. Monoliths were made in situ by photopolymerizing ethylene glycoldimethacrylate (EDMA) monomers in the presence of lauryl methacrylate (LMA) or butyl methacrylate (BMA) crosslinkers. 

FIGURE 27-20 Microfabricated columns (a) and chromatogram (b). The columns in (a) were 0.9-m-long spiral and serpentine channels, The mixture (b) was 1, acetone 2. 2-butanone 3. benzene 4, trichloroethylene 5. 2,5-dimethyl-furan and 6. toluene. Air was used as the carrier gas with an outlet pressure of 0.5 atm. (From R. Sacks, in Modern Practice of Gas Chromatography, R. L. Grob and E. F. Barry, eds., 4th ed New York Wiley-Interscience. 2004. p. 269. With permission.)... 

The third way to employ ion beams in lithography is to combine the first two techniques and use an ion optical column to project the image of the pattern of a stencil mask onto a wafer. This is called ion projection lithography (IPL), which was pioneered at Ion Microfabrication Systems (IMS) of Austria in the late 1980s.Because IPL is the most technologically important of the three versions of ion-beam lithographies, we shall discuss it in much greater detail. 

S. H. Cypes, J. R. Engstrom, Construction, analysis and evaluation of a microfabricated stripping column, 7 International Conference on Microreaction Technology,... 

CEC columns are generally made of fused-silica tubing, usually packed with the appropriate stationary phase. Today, the most commonly used CEC columns have i.d. of 100 p,m or less, with 50 and 75 p,m i.d. being the most popular. The stationary phase is retained in the column by two frits. Column designs can be categorized into two major types OT columns and packed structures, which include packed columns, monolithic columns, and microfabricated stractures (open or continuous beds). Packed capillary columns are most commonly used, as has been demonstrated in numerous papers [9-11]. They can be subdivided into three different categories columns packed with particles, columns with continuous beds fabricated in situ creating a rod-like monolithic structure, and columns with immobilized or entrapped particulate materials. 

Beard, N. R, Zhang, C-X., and deMello, A. J. In-column fleld-amplified sample stacking of biogenic amines on microfabricated electrophoresis devices. Electrophoresis 24, 732, 2003. 

Haab, B.B. and Mathies, R.A., Single-molecule detection of DNA separations in microfabricated capillary electrophoresis chips employing focused molecular streams. Anal. Chem., 71,5137, 1999. Jacobson, S.C., Hergenrdder, R., Koutny, L.B., Warmack, R.J., and Ramsey, J.M., Effects of injection schemes and column geometry on the performance of microchip electrophoresis devices. Anal. Chem.,... 

In a more direct translation of current macroscale, silica-based, SPE protocols other, microchip-based purification systems have focused on utilizing a packed silica-bead bed or silica sol-gel matrix solid phase for purification. This type of extraction was first miniaturized in a capillary format, to demonstrate the utility of the proposed method in the microscale, by Tian et al., who utilized a 500 nL capillary-based chamber packed with silica particles to establish that PCR-amplifiable DNA (with 80-90% of proteins removed during the load and wash steps) could be obtained from white blood cells with high extraction efficiencies (70%). This demonstrated the feasibility of incorporating such silica-based column purification methods into microfabricated devices and the effectiveness of such methods for the purification of DNA from a wide variety of biological species (white blood cells, cultured cells, and whole blood). 

In contrast to columns, the microfabricated devices feature a network of microchannels etched in glass or imprinted in a polymer plate that are designed to enable much smaller sample volumes to be analyzed at an increased speed and permitting a large number of analysis to be performed simultaneously, thus increasing the overall throughput. Microfluidic analytical devices with open channel geometry are currently most frequently used to achieve the desired functions. Open channels are best suited for separation systems in which no interactions with functionalities located at the solid surface are required or are even undesirable, such as in electrophoresis. 

For volatiles and semivolatiles with vapor pressures too low to be detected by direct IMS introduction methods, preconcentration techniqnes are often anployed. The most common approach is to pack a glass tube or stainless steel column with an adsorbing material such as Tenax or Carbosieve. Other methods, such as micro-fabricated adsorbents, have also been proposed, bnt these microfabricated concentrators are relatively new, with limited field exposnre. Nevertheless, for handheld and mini-IMS instruments, these preconcentration devices appear promising, offering rapid concentration and desorption with low power. ... 

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