The theoretical-plate concept in chromatography has been treated on the basis of continuous flow of eluent through the plates of the column. A treatment more'precise in principle than the previous treatments is presented. General elution and deposition equations have been derived and applied to special cases of practical interest. The derived formulas have the advantage of precision, generality, and simplicity.The theory was found adaptable to the treatment of gradient elution and also to the calculation of the fraction of solute which has been eluted or still-adsorbed on the column during the elution process.A method for the determination of the number of theoretical plates in a chromatographic column is also described.The similarity bct\vccn thc chromatographic and the distillation and extraction fractioning columns has becn realized for a long time, but it was only rccestly that theories of chromatography based on the concepts which had been developed for distillation were worked out in detail.The first detailed theory of chromatography using the concepts developed for distillation was offered by Martin and Syiigc in 1941 (5). They were able to give a picture of the coriccntration of solute at any t.ime and place in the column. Their treatment was based on a continuous-flow model of the mobile phase through the In 1947 Mayer and Tompkins (6) appliod a pliite theory to the detcrmination of the coniposition of the eluate and to the prediction of the distribution of the various siit~starices on i.he column. Their thcory was b:iscd on a discontinuous model where a finite eluent volume is equilibrated step by step with one thcort!t,ical plate in the column after mother. They were :rble to derive an expression for the concentration distribution which they approximated to a11 error distribution for a large number of theoret.ical Martin and Synge, as well as Mayer and Tompkins, treated only the case where all the solute was deposited on the top plate of the column a t the beginriingof the elution process.In 1955, Glueckaiif (4) pointed out that t.he Mayer rrnd Tompkins discontiriuous model does not represent the physical picture of the process and would lead to large errors even if the number of theoreticnl plates were :IS high as 1,OOO. He derived a partial-differential equat.ion bascd 011 i~ continuous-flow model and solved the e quation to obtain an error distribution of solute on the column, but he Iiiid to assume a large number of thcoretical plates. IIe developed equiitionv 1)ot.h for the deposition process atid for thc chtion of a zone which wis evenly distributcd over a finite number of theoretical pkites.This present theory rclics on the same two basic assumptions as did thct previous plnks. pl:1tes. Present address, 630 West 16s Ptrert, S e w York, Kcw York. authors, namely, t h a t solutes adsorbed on the column have linear-adsorption isotherms add that the chromatographic column is equivalent to a certain number of theoretical plates. It is based on a continuous-flow model of eluent through thc plates, jus...

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This series is intended to present the basic theory of chromatography in simple and clear mathematics which can be readily followed by the average chemist. The basic ideas are not necessarily novel but the approach and applications should be original and of interest to a large number of workers in chromatography rather than being limited to a small number of highly qualified chromatographers of great mathematical ability. Peak Capacity and Resolution in Capillary Columns A. S. SaidThe Kuwait Institute of Applied Technology, Kuwait.The simple peak capacity and resolution equations derived for the packed column do not apply so well to capillary columns. The reason is that in the course of their derivation the assumption was made that the peak width is proportional to the retention volume, measured from the point of injection. This is a satisfactory assumption in the case of a packed column but is not valid for capillary columns. Thus for a packed column (3)The only difference is that in the case of n, the subscripts 1 and 2 refer to any two points on the chromatogram and in the case of R they refer to the uncorrected retention volume, width and capacity ratio for the two neighboring peaks under consideration. As pointed out in reference[2], R may be defined as being the peak capacity between the maximum points of the two overlapping peaks.