Electrokinetic injection platform

Research stiU continues into the development of enhanced electrokinetic injection techniques for p-chips. Modifications made to the outlet end of the separation channel, such as its connection to a length of fused silica capillary to facilitate chip interfacing with off-chip detection systems for example, can be adopted equally well for chip inlets and sample introduction. The use of conventional capillary to interface between macroscale sample reservoirs and p-chip platforms has been successfully... 

Figure 14. Microfluidic realization of capillary electrophoresis analysis on the electrokinetic platform. (Adapted from [123], ( Agilent Technologies, Inc. 2007. Reproduced with permission, courtesy of Agilent Technologies, Inc.) After the sample has been transported to the junction area (a) it is metered by the activated horizontal flow and injected into the separation channel (b). Therein, the sample components are electrophoreticaUy separated (c) and readout by their fluorescence signal (d). The complete microfluidic CE-chip is depicted in the center.

The hrst pTAS devices were based on GC. Soon after, HPLC-based pTAS platforms began to appear and then CE followed. In chip CE, an injection was performed and an electrophoretic separation of a sample mixture (different fluorescent dyes) and all liquid handling was achieved using electro-osmotic flow. Since then, electrophoresis and electrokinetic fluid handling have been the cornerstones of many miniaturised analytical devices. 

Related to the assessment of heavy metals which are alarming in foods, ME-AD approach has also been reported for their determination in juice samples [38], East detection of prominent heavy metals (lead, cadmium, and copper) has been demonstrated on ME-AD platforms using CSPEs. Chemical separation (25 mM MES/L-histidine buffer solution of pH 7.0), electrokinetic conditions (-1-1200 V, 3 s injection), and detection potential (-0.8 V) were carefully optimized. Excellent recoveries in spiked juice samples (without oxygen-free condition) ranging from 92% to 108% (n = 10) were obtained, giving in addition an excellent reproducibility (RSDs < 7%). 

Microfluidic platforms can be considered as an ideal tool for electrochemical sensing. One of the main reasmis lies in is capability to perform microscale flow-injection analysis. This concept includes electrokinetic or hydrodymanic injection, pumping, and analyte detection using the microfluidic platform as a microchip format to prevent interconnections and dead volumes. This approach is clearly advantageous since it allows accurate, ultrasmall sample volumes (loop-size variable) to be introduced and has accurate fluid-control and manipulation capabilities. 

---