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the Poisson curve. Consider the elution curve as shown in Figure 9. The origin of the Poisson curve is the point of injection, whereas the origin of the Gaussian curve is at the peak maximum, which will be (n) plate volumes from the injection point.  Now, a point X, (v)  plate  volumes  from the point of injection will be (v-n) = w plate volumes from the peak maximum. Consequently, v = (n+w). This change of origin is depicted in Figure 9. Now, the Poisson form of the elution equation is as follows,                                      Figure 9.  The Different Axes of The Poisson Elution Curve and the Gaussian Elution Curve

onto a column. The first component to elute, (A), will be that solute held least strongly in the stationary phase. Then the second solute, (B), will elute but it will be mixed with the first solute. Finally, the third solute (C), will elute in conjunction with (A) and (B). It is clear that only solute (A) is eluted in a pure form and, thus, frontal analysis would be quite inappropriate for most practical analytical applications. This development technique has been completely superseded by elution development. Elution Development Elution development is best described as a series of absorption-extraction processes which are continuous from the time the sample is injected into the distribution system until the time the solutes exit from it. The elution process is depicted in Figure 1. The concentration profiles of the solute in both the mobile and stationary phases are depicted as Gaussian in form. Equilibrium occurs between the two phases when the

with primary and secondary amino functional groups, under mild conditions (55˚C for 10 min.), in the presence of triethylamine, to produce the corresponding fluorescent thiourea derivatives. The purity of the reagents were ascertained by separation on a cyclodextrin column and the results are shown in figure 50. The separation was carried out on a derivatized cyclodextrin column (ES-PhCD) 15 cm long and 6 mm I.D., packed with 5 mm particles. Chromatogram A shows the elution of the (R)-(–)-NBD-PyNCS isomer, B, the elution of the (R)-(+)-NBD-PyNCS isomer and C, the separation of the racemic mixture. The mobile phase was a mixture of acetonitrile/methanol/water : 3/3/4 v/v/v. Chromatogram D shows the elution of the (R)-(–)-DBD-PyNCS isomer, E, the elution of the (R)-(+)-DBD-PyNCS isomer and F, the separation of the racemic mixture. In this case, the mobile phase consisted of a mixture of acetonitrile/water : 8/2 v/v. It is seen that the cyclodextrin based

The time taken to achieve these efficiencies when eluting the last peak at a k' value of 10 can be calculated employing equation (45). The results obtained are shown in figure 4 where the elution time obtained from columns of maximum efficiency are plotted against particle diameter.   Figure 14. Graph of Log. Elution Time against Particle Diameter On examination of the curve in figure 14, the problem associated with high efficiencies becomes apparent. The elution time for the short column having about 3500 theoretical plates is only just about one half minute. The elution time from the 1.5 million plate column, however, is about 54 days, a rather long time to wait

The chromatogram that depicts the elution of a solute is a graph relating the concentration of the solute in the mobile phase leaving the column to elapsed time. However, at a constant flow rate, the chromatogram will also relate the solute concentration to the volume of mobile phase passed through the column. In figure 1, is shown the elution of a single peak. The expression, f(v), is the elution curve equation and this will be derived using the plate theory. Figure 1. The Elution Curve of a Single Peak   Once

Column Efficiency The column efficiency is defined as the number of theoretical plates in the column. As discussed in the plate theory, the faster the equilibrium process, the smaller the plates and thus, the greater the number of plates in the column. It is therefore important to know how to determine the number of plates a column possesses and the relationship of the number of theoretical plates in the column to the properties of the chromatogram. Starting with the Poisson form of the elution equation, the peak width at the points of inflexion (which corresponds to twice the standard deviation of the normal elution curve) can be found by equating the second differential of the elution equation to zero and solving in the usual manner. Thus, at the points of inflexion,