High microchip columns

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). 

Monolithic silica is the most recently introduced class of stationary phases for electrochromatography on microchips. They benefit from their very high surface area, adjustable pore size, and controllable surface chemistry. Functionalities required for the separation in reversed-phase mode are typically incorporated onto the silica monolith by including an appropriate silicon alkoxide in the precursor mixture or by silanization of the surface after the monolith has been formed. Monolithic silica-based columns are generally known to exhibit superior performance in HPLC separations of small molecules, which is atftibuted to the presence of mesopores entailing large surface areas. 

Two-dimensional (2D) separation systems are of interest because of their increased peak capacity over one-dimensional separations. Microfabricated devices (microchips) are potentially useful for multidimensional separations because high-efficiency separations can be achieved and small sample volumes can be manipulated with minimal dead volumes between interconnecting channels. Various techniques may be adopted for the fabrication of chromatographic columns in microchips for p-CEC following integration with other orthogonal separation methods as well as sample pretreatment proaches for rapid, automated analysis of more complicated biosamples with possible coupling to mass spectrometric detection. 

Mogensen KB, Chen MX, Molhave K, Boggild P, Kutter JP (2011) Carbon nanotube based separation columns for high electrical field strengths in microchip electrochromatography. Lab Chip 11 2116-2118... 

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