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Let the distance between the injection point and the peak maximum (the retention distance on the chromatogram) be (y) cm and the peak width at the points of inflexion be (x) cm. If a computer data acquisition and processing system is employed, then the equivalent retention times can be used. Now, it has already been shown that the retention volume of a solute is given by n(vm + Kvs), and twice the standard deviation of the peak at the inflexion points is given by Thus, by simple proportion,           &

a peak measure at 0.6065 of the peak height (ca 0.607h). The peak width measured at this height is equivalent to two standard deviations (2s) of the Gaussian curve and thus has significance when dealing with chromatography theory. The peak width at half height (w0.5) is the distance between each side of a peak measured at half the peak height. The peak width measured at half height has no significance with respect to chromatography theory. The peak width at the base (wB) is the distance between the intersections of the tangents drawn to the sides of the peak and the peak base geometrically produced. The peak width at the base is equivalent to four standard deviations (4s) of the Gaussian curve and thus also has significance when dealing with chromatography theory. Factors Controlling Retention The equation for the retention volume (Vr), as derived from the Plate theory (see ThePlate Theory and Extensions ) is as follows

with a high concentration at the sharp front of the following peak, and thus significant contamination of the second peak will occur. The results of the overload experiment are better examined quantitatively. Curves relating the retention distance of the front and back of each peak to the sample load are shown in figure 8.The retention distances of the front and back of each peak (measured at the points of injection, 0.6065 x peak height) are shown plotted against sample mass. The change in retention with mass of benzene injected is clearly demonstrated, the maximum effect being for the solute anthracene (the last eluted peak ) and the minimum for benzene itself. It is interesting to note that there is little change in the band width of the last eluted peak anthracene.   After J. Chromatogr., Ref. (3)   Figure 8. The Effect of Mass Overload of Benzene on the Retention of Benzene, Naphthalene and Anthracene

nbsp; It is seen from figure 4 that the peak front of each solute has a constant retention irrespective of the volume of charge.� The back of the peak, however, only maintains a constant retention distance up to a sample volume of 0.5 ml for the three component mixtures, and up to 1 ml for the two component mixture. Subsequent to these limiting sample volume values, the retention of the back of the peak appears to increase linearly with charge volume. It is also interesting to note that peak dispersion is the same for each solute and is independent of the nature of the solute or its capacity ratio (k'). The peak dispersion towards greater retention is characteristic of volume overload

from equation 2 was 6.1 ml). Destefano and Beachel (4) has also investigated the effect of volume and mass overload on resolution. They concluded that, given the choice, it is advantageous to overload a column with a large volume of a dilute solution of sample, as an alternative to using a small volume containing a high concentration of sample. They reported, however, that the validity of this conclusion, appeared to depend somewhat on the capacity ratios of the eluting solutes. In figure 4 the retention distance (measured in cm along the chart) is plotted against the sample volume After, J. Chromatogr., Ref. [3]   Figure 4. Retention Distance of Benzene, Naphthalene and Anthracene against Sample Volume

nbsp;                                             where (y) is the retention distance and (x) is the peak width. Now, the number of effective plates  (NE), by definition, is given by                                                           &