In chromatography, a solute moves through a chromatographic column and tends to spread, forming a Gaussian-shaped band. The longer the solute spends in the column, the broader the band becomes. The broadening can lead to overlaps within the column, affecting separation effectiveness.

The effectiveness of separation can be evaluated by determining the level of separation between two neighboring peaks in a chromatogram, which represents the individual components of a sample.

In chromatography, the resolution is expressed as the retention time or volume difference ratio between two adjacent peaks to their average base width. A higher resolution indicates better separation between peaks.

Resolution value is a quantitative measure of a column's ability to separate two analytes. It indicates the distance between two peaks relative to their widths. A resolution of 1.0 results in a 2.3% overlap of two equal-width peaks, which is the minimum separation required for accurate quantitation. A resolution of 1.5 corresponds to a 0.1% overlap of equal-width peaks, which is considered adequate for baseline resolution of equal-height peaks.

At lower resolutions, the overlap in elution time and volume between two adjacent peaks is high, meaning significant co-elution of the two solutes. As the resolution increases, the area of overlap decreases.

Since Gaussian curves have a predictable form, the equation can be adjusted for the width at half the maximum peak height if measuring the base width is challenging. In addition, resolution can be calculated using the separation factor, also known as selectivity. This is a thermodynamic measure of the relative retention of two solutes, expressed as the ratio of their retention factors.

The master resolution equation or the Purnell equation connects resolution to efficiency. Resolution can be improved by extending the retention time or reducing the baseline widths of the solutes. Increasing retention time can be achieved by enhancing the solutes' interaction with the column or by raising the column's selectivity for one of the solutes. Adding more theoretical plates to increase the number of separation stages can also improve resolution by increasing the column length. However, this also increases the time required for separation.

In packed columns, the bandwidths increase with the square root of the distance migrated. Meanwhile, the distance between the centers of the peaks increases linearly with the distance traveled. This means the separation improves as the bands or peaks move faster than the broadening.