Experimental Considerations

If higher concentrations of buffer are used, particularly with high concentrations of organic solvent, then bubble formation can become a problem. This can be overcome by operating the whole capillary under pressure. Figure 4 is a schematic diagram showing such a pressurized apparatus.

The packing of small-diameter particles into narrow capillaries represents an enormous challenge. The initial stage is the formation of a suitable retaining frit, which must be capable of retaining particles of not more than 1 |im and also capable of withstanding pressures of the order of 10 000 psi (68 000 kPa). Outline details of how to form such frits can be found in the literature. The frits must have a good porosity if the packing process is to be successful; porosity can be tested with a conventional HPLC pump at 6000 psi (41000 kPa) and a flow of water of

Figure 4 Schematic layout of the pressurization system for electrochromatography. (By permission of the author.)

1 mL min"1. For a good frit the pressure should rise to 6000 psi fairly rapidly and then stop due to the pressure cut-out. An ideal frit is one where the pressure decays to zero over a period of 10-20 s. If the pressure decay is much quicker then the frit has probably failed; if the decay is very slow then the frit is not porous enough for efficient column packing. Once a satisfactory frit has been formed, then the capillary can be slurry packed as outlined in Figure 5.

Although the packed capillary contains water it is not necessary to condition it with mobile phase since there is a sufficient EOF to allow the mobile phase to be pumped into the system. Once a steady current has been established the column is ready for use.

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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