Liquid Chromatography Blog

Back-to-Basics #1: Retention Factor

This technical article looks at some of the basic calculations used in HPLC, with an emphasis on their practical utility for evaluating separations, developing methods and isolating problems. The first in line is the retention factor, k, often called the capacity factor, k’. 

The calculation is a simple one. t R is the retention time and t 0 is the column dead-time. Retention is measured from the time the sample is injected to the highest point on the peak. Measurement of the column dead-time is most easily measured as the first disturbance in the chromatogram (the “solvent front”) – we’ll consider t 0 more later. As both t R and t 0 are in the same units (min, sec, furlongs or fortnights), the units cancel out and k is a dimensionless quantity.

By reading the full article, you will learn more about the retention factor as a measure of the distribution of the sample between the mobile phase and the stationary phase. 

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