Practical Considerations

Perhaps the key practical consideration is whether integrated on-chip detection will be employed, or whether the separated compounds will be transferred to another device, such as a mass spectrometer. In a similar context to conventional capillary electro-phoresis separations, on-chip detection is the ideal option, since it minimizes dispersion and the dead volume associated with the transfer of analytes from the chip to a detector. The dead volume will normally be far in excess of the separation volume, thus band broadening will be a serious problem.

The other key issue is sample introduction. The simplest system relies on the EOF to introduce the sample into the separation capillary. Consider the channel arrangement in Figure 4. The channels are etched into silica, and no deactivating treatment is applied. Under normal conditions (I), the applied voltage between reservoirs A and B induces EOF. In addition, the potential field gradient will give rise to electrophoretic separations.

Since only buffer is flowing, this does not give rise to any apparent separation effect. When the voltage is manipulated such that it is now between reservoirs C and D (II), EOF is induced between the reservoirs, thus the sample is introduced, and occupies a small section of the main channel. Once the voltage is restored between A and B, the separation step begins (III). Here, the sample is moved by the EOF towards reservior D, and separation occurs due to elec-trophoretic mobility.

In situations where EOF is insignificant due to the absence of surface charge, the injection step relies either on the electrophoretic movement of the analytes or an applied pressure. There is, of course, a potential problem with electrophoretic mobility, and that is the discriminatory effects observed between analytes of high and low electrophoretic mobility. Pressure, on the other hand, offers a simple

Figure 4 Sample introduction into the separation channel. (I) When the voltage is applied between reservoirs A and B, the separation channel is filled with running buffer. (II) To inject a sample, the voltage is applied between C and D: the sample moves into a short section of the separation channel. (III) With the voltage restored across A and B, the sample moves along the separation capillary, and separation occurs.

Figure 4 Sample introduction into the separation channel. (I) When the voltage is applied between reservoirs A and B, the separation channel is filled with running buffer. (II) To inject a sample, the voltage is applied between C and D: the sample moves into a short section of the separation channel. (III) With the voltage restored across A and B, the sample moves along the separation capillary, and separation occurs.

and nondiscriminatory route for sample introduction. This can be achieved by either applying pressure to one reservoir in order to force the analyte through the system, or by deformation of the chip (in situations where the polymer is flexible). In either case, a valve-less injection method is used; this greatly simplifies the operational aspect of these systems.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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