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The development of a reliable sample injector for CE
For a long time the creation of a sample plug of constant and reliable volume is one of the most critical steps in analytical chemistry, especially when the application prohibits the use of an internal reference standard. When capillary electrophoresis (CE) is performed in microfluidics devices, a double T injection cross is often used in combination with an electrokinetic transportation mechanism. An example of such an injection procedure is given in the scheme below: A chip consisting of channels, reservoirs and a detector (1) is filled with a background electrolyte (2), a sample is applied (3) and using an electric field charged species are driven into the channel (4). When a representation of the applied sample is formed in the double T injection cross, the electrical field direction is changed, moving the sample plug into the separation channel (5) where the CE separation process takes place (6+7), enabling the detection of separated zones at the detector site (8).
The volume and shape of the sample plug in the injection cross is as already stated of critical importance for the quantitative outcome of the analysis. However, the volume and shape often vary due to amongst others variations in geometry, sample composition, temperature and applied voltage. To achieve better accuracy in quantitative CE analysis the impact of these variations on the outcome of the analysis needs to be reduced.
Your assignment is both theoretical and practical: to find out which variations have the largest negative influence, to design chips where the sample plug can be fully controlled by electrical means, and to measure with these chips to demonstrate the improvements.
You will be supervised in the BIOS/Lab-on-a-Chip group (Jan Eijkel). Arjan Floris of the UT startup Medimate will also be advising you. Your work can be of direct potential benefit for Medimate, which manufactures CE analysis equipment for clinical diagnostics.
Contact: Jan Eijkel, Hogekamp 6144, tel. 053 4892839, email j.c.t.eijkel@utwente.nl
Some reading material:
