Fluorescence detection capillary isotachophoresis

A variety of formats and options for different types of applications are possible in CE, such as micellar electrokinetic chromatography (MEKC), isotachophoresis (ITP), and capillary gel electrophoresis (CGE). The main applications for CE concern biochemical applications, but CE can also be useful in pesticide methods. The main problem with CE for residue analysis of small molecules has been the low sensitivity of detection in the narrow capillary used in the separation. With the development of extended detection pathlengths and special optics, absorbance detection can give reasonably low detection limits in clean samples. However, complex samples can be very difficult to analyze using capillary electrophoresis/ultraviolet detection (CE/UV). CE with laser-induced fluorescence detection can provide an extraordinarily low LOQ, but the analytes must be fluorescent with excitation peaks at common laser wavelengths for this approach to work. Derivatization of the analytes with appropriate fluorescent labels may be possible, as is done in biochemical applications, but pesticide analysis has not been such an important application to utilize such an approach. 

In isotachophoresis, electrical detection is most commonly used, although thermal and UV-absorption detection are also used(3). For capillary zone electrophoresis, UV-absorption and fluorescence detection have proven most useful so far. The principles behind the optical detection modes are fairly obvious. However, the electrical and thermal detectors deserve further explanation. As described earlier, in isotachophoresis, each zone is an individual "pure" band of sample ions. The zones travel in order of decreasing mobility. To compensate for each successive... 

ITP, also known as displacement electrophoresis, was first performed in capillary tubes by Ever-aerts et al. [69] for the separation of strong anions using a thermocouple detector. Since then, ITP has been used for the analysis of various important chemical and biological species such as amino acids [70], peptides [71], nucleotides [72], proteins [73,74], heavy metal ions [75], and other organic/inorganic ions [76,77] on a variety of detection platforms such as UV absorbance, conductivity and fluorescence detection. Over the past 15 years, ITP has been used as a preconcentration technique in conjunction with CE [78]. This mode of ITP, referred to as transient isotachophoresis (tITP), has been implemented on microchip platform in the recent years to achieve improved sensitivity [22,79,80]. 

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