The Resolving Power of an LC Column

It has already been stated that for two solutes to be resolved their peaks must be moved apart in the column and, at the same time, maintained sufficiently narrow to permit them to be eluted as discrete peaks. The criterion for two peaks to be resolved is arbitrary, but as stated in Chapter 1, resolution is is usually defined as the ratio of the distance between the peaks, to the peak width at the points of inflection. The separation of a pair of solutes on columns of differing resolution is shown in figure (2). 

It is seen that for base-line resolution the peak maxima must be six standard deviations (6a) apart. But for accurate quantitative analysis, employing peak heights measurements, a separation of (4o) is usually quite adequate. Even when peak area measurements are employed, a separation of (4o) will usually provide adequate accuracy, particularly if computer data acquisition and processing is employed with modern software. Therefore, throughout this book, whenever dealing with resolution, or column design, a resolution of (4o) will be assumed. 

It should be pointed out that two adjacent peaks from solutes of different chemical type or significantly different molecular weight will not necessarily have precisely the same peak widths. However, the difference will be relatively small and, in the vast majority of cases, will be 

Consider the two peaks depicted in the now well recognized figure (3). The difference between the two peaks, for solutes (A) and (B), measured in volume flow of mobile phase will be, 

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