GC021 Plate number and Peak Width

A broadening of peaks with retention time is a natural phenomenon of the chromatographic process. Due to this fact, the most common measure of efficiency is the plate number, N, defined as:

N = (tR/S)^2 = 16(tR/Wb)^2 = 5.54(tR/W_(1/2))^2

Where W_(1/2) is the width of the peak measured at half its height

N is unitless. A high value of N indicates an efficient column, a very desirable quality. If the chromatogram has several peaks, the value of N for each compound will vary. However, it is common practice to assign a value to a column, based only on one measurement.

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