Gated Interface for HPLC-CE

Because of the small volumes encountered in CE, implementing CE as a second dimension is difficult if a valve is used. More efficient, lower volume unions have been utilized in a number of cases. The main types of these interfaces include optical gating and flow gating, which are discussed below. Electrical gating is described in detail in Chapter 15. Fraction collection is also used, as discussed in Chapter 16, although this takes longer and is a less efficient method than the other comprehensive 2D schemes. Chip-based separation systems typically use some form of electrical gating and these systems will be discussed below. 

OGI techniques have been used extensively in single capillary systems where a narrow injection width is needed along with a simplified interface. These techniques are summarized by Hapuarachchi et al. (2006). There are many advantages to this 

FIGURE 5.9 The flow gating interface from Hooker and Jorgenson (1997). The cross-flow of buffer prevents LC effluent from electromigrating onto the CE capillary until an injection is desired. This figure is used by permission of the American Chemical Society. 

Chip-based systems that employ microfluidics have become a popular research area and a number of systems are now available commercially that utilize electrophoresis- 

The use of electrically-gated solute injection into the electrophoresis system simplifies the chip design as electrical connections are easy to implement as compared to the microfluidics part of the chip. Voltage waveform manipulation via hardware and software are relatively easy to control and implement. 

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