Capillary high-voltage supply

Fig. 16.1. Schematic of a CEC instrument. The capillary column is typically 20-50 cm long with an inner diameter of 50-100 pm. The high voltage supply normally delivers 0-30 kV. About 1-10 nL of sample is usually injected electrokinetically.

A CEC instrument basically consists of a system for injection (pressure driven or electrokinetic), a column in which the separation takes place, a detector and a high voltage supply (Fig. 16.1). The most commonly used detector so far has been UV with transmission through the capillary outside of the packed bed. Laser induced fluorescence detection has been employed in several studies. Also, mass-spectrometry has been used. Normally, isocratic CEC is performed, but approaches to gradient CEC have been reported [29]. However, special equipment must be employed in most cases. 

Buffer Reservoirs. These containers hold the buffer solution that provides for a complete electrical circuit through the capillary and connection to the high-voltage supply. Due to electro-osmotic flow as described earlier, the vials also serve as reservoirs to maintain electroneutrality in the system. 

FIG U RE 1.1 Photograph of the CE system designed by Hjerten. On the left are stacked the high voltage supply and electronic components for the detector, topped off by a strip-chart recorder. In the center is the carriage with the capillary and the electrode vessels above the immersion bath, while the cooling reservoir flanks it on... 

Electrochemical Techniques, Fig. 1 Schematic of capillary electrophoresis with electrochemical detection system. (a) High-voltage supply, (h) grounded platinum electrode, (c) reference electrode, (d) auxiliary platinum electrode, (e) detection electrode, (/) running buffer, (g)... 

High Voltage Power Supply Separation Capillary Detection Capillary ... 

The simplest CEC equipment must include the following components a high-voltage power supply, solvent and sample vials at the inlet and a vial to collect waste at the outlet of the capillary column, a column that simultaneously generates EOF and separates the analytes, and a detector that monitors the component peaks as they leave the column. Figure 4 shows a scheme of an instrument that... 

A schematic representation of a CE system is presented in Figure 9.1. In this diagram, the CE components have obvious counterparts to those found in slab gel electrophoresis. Instead of buffer tanks there are two small buffer reservoirs, and the capillary takes the place of the gel (or more accurately, a gel lane). The capillary is immersed in the electrolyte-filled reservoirs, which also make contact with the electrodes connected to a high-voltage power supply. A new feature to the conventional gel electrophoresis format is the presence of an online detection system. 

CE instrumentation is quite simple (see Chapter 3). A core instrument utilizes a high-voltage power supply (capable of voltages in excess of 30,000 V), capillaries (approximately 25—lOOpm I.D.), buffers to complete the circuit (e.g., citrate, phosphate, or acetate), and a detector (e.g., UV-visible). CE provides simplicity of method development, reliability, speed, and versatility. It is a valuable technique because it can separate compounds that have traditionally been difficult to handle by HPLC. Furthermore, it can be automated for quantitative analysis. CE can play an important role in process analytical technology (PAT). For example, an on-line CE system can completely automate the sampling, sample preparation, and analysis of proteins or other species that can be separated by CE. 

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