Joule Heating
The conduction of electric current through an electrolytic solution generates heat via frictional collisions between migrating ions and buffer molecules. Since high field strengths are employed in HPCE, ohmic or Joule heating can be substantial. There are two problems that can result from Joule heating 1. Temperature changes due to ineffective heat dissipation 2. Development of thermal gradients across the capillary If heat is not dissipated at a rate equal to its production, the temperature...
Electroendoosmosis
One of the fundamental processes that accompanies electrophoresis is electroos-mosis. One of the pumping mechanisms of HPCE, electroosmosis occurs because of the surface charge, known as the zeta potential, on the wall of the capillary. Fused silica is the most common material used to produce capillaries for HPCE. Technology developed for manufacturing capillary columns for GC readily transferred to HPCE. Fused silica is a highly crosslinked polymer of silicon dioxide with tremendous tensile...
N Uqe
a 1,000,000-plate separation on a 50-cm capillary gives a1 0.25 mm2. For a 100,000-plate separation, lt 72 2.5. Thus, it is reasonably simple to maintain the efficiency for a 100,000-plate separation, but quite difficult when the plate count approaches 1,000,000. Some of the key sources of dispersion along with their importance and remedy are given in Table 2.7. On-capillary dispersion comprises contributions from injection overload, hydrostatic flow siphoning , diffusion, adsorption wall...
Instrumentation
The instrumental configuration for HPCE is relatively simple. Before 1988, all work was done on simple homemade systems of a design similar to Jorgenson and Lukacs's original work 35, 59, 64 . A schematic of a homemade system is shown in Figure 1.7. The system consists of a high voltage power supply, buffer reservoirs, an HPLC ultraviolet detector, a capillary, and a Plexiglas cabinet. A safety interlock can be employed to prevent activation of high voltage when the cabinet is open. The...
Generic Hpce Systems
While application specific DNA systems are becoming wildly successful, generic HPCE systems have not provided the returns expected by the scientific instrument manufacturers. The generic HPCE system is designed for the user to develop his or her own methods. In HPLC, this type of system forms the largest segment of this multibillion dollar market. There are numerous reasons, beyond the scientific, that this has not occurred with HPCE. 1. Liquid chromatography HPLC is the greatest analytical...
Optimizing The Voltage And Temperature
A means of optimizing the voltage and or the temperature despite the buffer concentration and capillary cooling system is very desirable. An Ohm's law plot provides this tool with very little experimental work 35, 36 . Simply fill the capillary with buffer, set the temperature, vary the voltage, record the current, and plot the results. Some Ohm's law plots are shown in Figures 2.17 and 2.18 for an air-cooled and water-cooled temperature control system, respectively. Whenever the graph shows a...