Microseparation methods

The aim of this chapter is to cover the theoretical and practical aspects of capillary gel electrophoresis. It also provides an overview of the key application areas of nucleic acid, protein, and complex carbohydrate analysis, affinity-based methodologies, as well as related microseparation methods such as ultra-thin-layer gel electrophoresis and electric field-mediated separations on microchips. It also gives the reader a better understanding of how to utilize this technology, and determine which actual method will provide appropriate technical solutions to problems that may have be perceived as more fundamental. Micropreparative aspects and applications are discussed in Chapter 12. 

Coupling of Mass Spectrometry with Microseparation Methods... 

W. Wall, K. Chan and Z. El Rassi, Electrically driven microseparation methods for pesticides and metabolites. VI. Surfactant-mediated electrokinetic capillary chromatography of anihne pesticidic metabolites derivatized with 9-fluoroenylmethyl chloroformate and their detection by laser-induced fluorescence. Electrophoresis, 22, 2320-2326, 2001. 

Wet separation of plastics is a microseparation method in which a suspension medium is used to separate plastics with density higher or lower than the suspension medium. For example, water can be used as medium to separate PE from PVC or PET. In this case, special tanks are used in which various types of plastic flaks are mixed with water and then given a sufiicient time to position themselves in the most suitable way according to their density. Materials are subsequently extracted separately from the top or bottom. This method is, however, not suitable for separating PVC from PET, because they have similar density. 

Straub et al. (76) reported a method for the identification and quantification of penicillin G, ampicillin, amoxicillin, cephapirin, cloxacillin, and ceftiofur residues in milk using perfusive-particle liquid chromatography combined with ultrasonic nebulization electrospray mass spectrometry. According to this method, a 0.5 ml milk sample is diluted with an equal volume of a solution consisting of acetonitrile/water (1 1), and ultrafiltrated in a microseparation system with a 10000 da molecular mass cut-off filter. An aliquot of the ultrafiltrate is then analyzed on a 15 cm porous II R/H LC (7-8 m) perfusion analytical column using the chromatographic conditions shown in Table 29.3. Concentrations as low as 10 ppb could be readily determined in milk by electrospray mass spectrometric detection. 

LIF detection is the most sensitive optical method so far, but is hard to miniaturize in order to satisfy the ultimate goal of a microfluidic chip that assembles all analytical processes within one micrometerscale microstructure. Therefore, how to achieve the miniaturization of fluorescence detection on microdevices is becoming an active field for lab-on-a-chip research. Several examples demonstrate recent advances in miniaturized LIF detection on the microchip. In 2005, Renzi et al. designed a hand-held microchip-based analytical instrument that combines fluidic, optics, electrical power, and interface modules and integrates the functions of fluidics, microseparation, lasers, power supplies etc., into an... 

In spite of their great potential, neither of the two electrodriven chromatographic methods described in this section is very popular or widely used. The probable main reason for this is the great number of variables which affect the separation, rendering it difficult to obtain reproducible results routinely. Because of its reliance on electrically generated electroosmotic flow rather than pressure, EC bears great promise in microseparation systems ( lab-on-a-chip ) and quite likely will become much more popular in the near fumre. 

Researchers at Rutgers University [70] studied a method of PVC microseparation fi-om PET, by which PVC is subjected to a process of selective bulking that causes it to float. Such a method maybe applied for separating small quantities of PVC from large quantities of PET, as normally is the case in the U.S., but is... 

Many researchers have studied the interfacial science and technology of laminar flow in microfluidics [8]. Interfacial polymerization and the subsequent formation of solid micro structures, such as membranes and fibers in a laminar flow system, are very interesting techniques because the bottom-up method through polymerization is suitable for the formation of miniature structures in a microspace [3]. The development of such microstructure systems plays an important role for the integration of various microfluidic operations and microchemical processing [9]. For instance, membrane formation in a microchannel and further modification has a strong potential for useful functions such as microseparation, microreaction and biochemical analysis [8-10]. Here, we will introduce several reports on polyamide and protein membrane formation through interfadal polycondensation in a microflow. 

For example, tin and lead alkylates have been determined in soil, water, or muscle tissue with GC/MS after exhaustive alkylation or with thermospray [239], API [240], and ICP-LC/MS [244] methods. The ESI spectra of some tin compounds is given in Figure 36. The APIMS techniques have proven to be very successful, even with metals bound to proteins and enzymes [241] and. interfaced to microseparation techniques, even elements such as iodine [242] or phosphorus [243] can be determined quantitatively. 

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