Microchip capillary electrophoresis (CE) was one of the first techniques demonstrating the advantages of scaling down conventional instrumental techniques to a microfluidic format. By decreasing the length of the separation column from several decimeters to a few centimeters or less the duration of a single analysis is significantly reduced, much lower voltages can be used, and sample plug injection and detection can be integrated.
Micronit has a number of CE chips in its assortment that provide a quick means for developing new applications and systems. The X3550, T3550, X8050 and T8050 chips are aimed at applications using optical methods to detect the separated zones inside the chips. These chips differ by the use of either a crossing channel or double-T type geometry to introduce sample into the separation channel, and the length of the separation channel which is either 35 or 80 mm. The figure below shows an example separating eight fluorescently labeled amino acid in a X3550 chip. The second example shows a separation of a mixture containing 12 DNA probes with a size in the range of 166 to 481 base pairs.
Some compounds are difficult to detect using optical means or optical detection is disadvantageous because of the complexity. In that case end-column conductivity detection provides a good alternative. A distinction is made between capacitively coupled contactless conductivity detection (C4D) where the detection electrodes are not in direct contact with the electrolyte inside the chip and contact conductivity detection where there is a galvanic contact. Both techniques have their cons and pros but the foremost advantage of the former method is that the sensitive detection electronics are completely decoupled from the high voltage circuit that is used to generate the electric field needed for the separation. This significantly reduces the risk of interference caused for example by leakage currents between the instruments.
Micronit offers two off-the-shelf chips (T35100C4D and T80100C4D) that have been developed in close collaboration with eDAQ for use with their contactless conductivity detector. The figures below show some application examples including the separation of a mixture of alkaline and alkaline earth metal salts, and secondly a mixture containing a number of inorganic anions. Both separations were performed on a T35100C4D chip.
For more examples see e.g. the following publications:
- C. P. Fredlake et.al. “Ultrafast DNA sequencing on a microchip by a hybrid separation mechanism that gives 600 bases in 6.5 minutes”, PNAS 2008, 105, 476-481
- S. Fritzsche et.al. “Chip electrophoresis with mass spectrometric detection in record speed”, Lab Chip, 2010, 10, 1227-1230
- X. Lu et.al. “Non-Ionic, Thermo-Responsive DEA/DMA Nanogels: Synthesis, Characterization, and Use for DNA Separations by Microchip Electrophoresis”, J Colloid Interface Sci. 2011, 357, 345-353
- R. Tantraet.al. “μTAS (micro total analysis systems) for the high-throughput measurement of nanomaterial solubility”, Journal of Physics: Conference Series 2013, 429, 012011