Sample preconcentration techniques isotachophoresis

Whether the stacking technique is called field-amplified stacking, transient isotachophoresis, or sample self-stacking, the driving force in on-column sample preconcentration for charges species is the need to satisfy the initial KRF conditions. Under separation and sample matrix conditions where the KRF is difficult to determine, simply calculations such as flcut and a offer a rapid evaluation of conditions for optimal transient ITP. 

Isotachophoresis (ITP) was, like FASS, originally developed for CE, but it relies on zero EOF. ITP is a quantitative analytical separation technique in its own right, with a wide range of applications. It has also been successfully applied in conjunction with CE for both sample preconcentration and removal of highly abundant charged species, by coupling the FTP and CE columns. The first... 

FAS can be implemented on microchips in a very similar manner as capillary electrophoresis. However, the requirement of low ionic strength sample buffer for FAS puts limitation on its use as general preconcentration technique. Variations of the technique, such as transient isotacho-phoresis and micellar electrokinetic sweeping, have been more successfully used. Jung et al. reported (Mi-chip transient isotachophoresis... 

Several strategies have been described for the preconcentration of sample components present at low concentrations. These techniques include zone sharpening,28-29 on-line packed columns,30 and transient capillary isotachophoresis (cITP).31-32 Other standard laboratory techniques are often used, including solid-phase extraction, protein precipitation, ultrafiltration, etc. Two important points to keep in mind when selecting a concentration protocol are the sample requirements of the method and the potential selectivity on relative concentrations of sample components. The latter point applies to purity and concentration analysis. 

On-tube detection is almost universally used in CE, and the short detection path lengths provided by fused silica capillaries result in a 100- to 400-foId reduction in detection sensitivity compared with HPLC. Although various techniques are employed in CE to regain most of this sensitivity, detectivity remains a serious concern. Therefore concentration steps are often necessary in sample preparation for CE. It should be emphasized that some concentration techniques such as evaporation and lyophilization will not change the sample ion/salt ion ratio for nonvolatile salts, so no effective concentration is achieved when electromigration injection is used. The use of transient isotachophoresis has been proposed for on-line preconcentration of proteins prior to CZE separation [41,42],... 

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