Determination of the surface heat‐transfer coefficient in CE

Abstract

A knowledge of the heat-transfer coefficient, h(s), for the external surface of the capillary or the overall heat coefficient, h(OA), is of great value in predicting the mean increase in temperature of the electrolyte, DeltaT(Mean), during electrokinetic separations. For CE, traditional indirect methods of determining h(s) were time-consuming and tended to overestimate cooling efficiency; a novel method is introduced, which is based on curve-fitting of plots of conductance versus voltage to calculate several important parameters including DeltaT(Mean), h(s), the conductance free of Joule heating effects (G(0)) and the voltage that causes autothermal runaway, V(lim). The new method is superior to previously published methods in that it can be performed more quickly and that it corrects for systematic errors in the measurement of electric current for voltages <5 kV. These errors tended to exaggerate the cooling efficiency of commercial instruments so that the calculated increases in electrolyte temperature were smaller than their actual values. Axially averaged values for h(s) were determined for three different commercial CE instruments ranging from 164 W m(-2) K(-1) for a passively cooled instrument in a drafty environment to 460 W m(-2) K(-1) for a liquid-cooled instrument.

Concentration and fractionation by isoelectric trapping in a micropreparative‐scale multicompartmental electrolyzer having orthogonal pH gradients. Part 2

“…4, and trapping of the ampholytes was completed by 60 min. the expected value set by the isoelectric buffer of the anodic feed stream, iminodiacetic acid [6,7]. Since in the cathodic feed stream the concentration of PTS À decreased more rapidly than the concentration of BzTMA 1 (right panel in [6,7].…”

“…However, 2 W (causing an initial current of 9 mA and voltage of 219 V) could be maintained with the tenfold diluted feed (15 mM actual salt concentration). Figure 4 illustrates the disappearance of the salt constituents (which have comparable mobilities [7]) from the anodic (left panel) and cathodic (right panel) feed streams, respectively. BzTMA 1 was removed from the anodic feed stream faster than PTS À because the field strength in the pH 2 anodic membrane was lower than in the membranes that flank the anodic sides of the collection compartments [6,7].…”

“…Figure 4 illustrates the disappearance of the salt constituents (which have comparable mobilities [7]) from the anodic (left panel) and cathodic (right panel) feed streams, respectively. BzTMA 1 was removed from the anodic feed stream faster than PTS À because the field strength in the pH 2 anodic membrane was lower than in the membranes that flank the anodic sides of the collection compartments [6,7]. PTS À was removed from the cathodic feed stream faster than BzTMA 1 because the field strength in the pH 10 cathodic membrane was lower than in the membranes that flank the cathodic sides of the collection compartments [6,7].…”

“…the expected value set by the isoelectric buffer of the anodic feed stream, iminodiacetic acid [6,7]. Since in the cathodic feed stream the concentration of PTS À decreased more rapidly than the concentration of BzTMA 1 (right panel in [6,7]. Overall, it took about the same time (60 min) to remove the salt and isolate the ampholytes into their respective compartments whether a combination of undiluted feed and lower initial power loads or diluted feeds and higher initial power loads were used.…”

“…BzTMA 1 was removed from the anodic feed stream faster than PTS À because the field strength in the pH 2 anodic membrane was lower than in the membranes that flank the anodic sides of the collection compartments [6,7]. PTS À was removed from the cathodic feed stream faster than BzTMA 1 because the field strength in the pH 10 cathodic membrane was lower than in the membranes that flank the cathodic sides of the collection compartments [6,7]. Once the majority of the strong electrolyte ions were removed (after about 40 min of IET), electrophoretic transport of the ampholytic sample components resumed at the same speed as in Fig.…”