# Chromatography Theory

## Introduction

The underlying principles that determine chromatographic separations are dynamic behaviors that depends on partitioning and mass transport.
These phenomena are too complex to model directly, and chromatography theory consists of empirical relationships to describe chromatographic columns and the separation of peaks in chromatograms.

## Description of Chromatograms

The retention of an analyte by a column is described by the capacity factor, k', where:

k' = t_{r} - t_{m}
-------
t_{m}

where t_{r} is the time for the analyte to pass through the column, and t_{m} is the time for mobile phase to pass through the column.
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## Description of chromatographic columns

The resolution of chromatographic columns is described by the theoretical plate height, H, or the number of theoretical plates, N. These two quantities are related by:

N = L / H

where L is the length of the column.

H and N provide useful measures to compare the performance of different columns for a given analyte. Useful expressions are:

H = L W^{2} / 16 t_{r}^{2}

and

N = 16 (t_{r} / W)^{2}

where W is the width of the peak at its base.

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