Surface area measurements, column experiment

In on-colnmn detectors, the working electrode is actually inserted into the tube used to make the column as illustrated in Figure IB. (Technically, these are not truly on-column detectors unless the stationary phase actually extends to the end of the tube however, for this discussion, on-column wiU refer to the case of the electrode inserted into the same tube used for the column.) The first on-column electrochemical detector was a 1 pm tip potentiometric, ion-selective electrode inserted into the ontlet of a 25 pm i.d. OTLC column [15]. The detection cell volume of 20 fL was proportional to the surface area of the electrode and the length of the stagnant diffusion layer from the electrode surface. Unlike the end-column detector, experiments demonstrated that the on-column detector did not cause a measurable loss in theorical plates. Little follow-up on use of micro-potentiometric electrodes as detectors has been reported. 

Parallel to the measurements of the effective surface area, the pressure drop of the packing is also investi ted by using a differential manometer, with accuracy 0.1 Pa. The column diameter was 470 mm. The height of the packing in all experiments was 2400 mm. A special liquid phase distributor was used... 

Since capillary tubing is involved in osmotic experiments, there are several points pertaining to this feature that should be noted. First, tubes that are carefully matched in diameter should be used so that no correction for surface tension effects need be considered. Next it should be appreciated that an equilibrium osmotic pressure can develop in a capillary tube with a minimum flow of solvent, and therefore the measured value of II applies to the solution as prepared. The pressure, of course, is independent of the cross-sectional area of the liquid column, but if too much solvent transfer were involved, then the effects of dilution would also have to be considered. Now let us examine the practical units that are used to express the concentration of solutions in these experiments. 

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