Retention distance (denoted ) is a concept in thin layer chromatography, designed for quantitative measurement of equal-spreading of the spots on the chromatographic plate and one of the chromatographic response functions. It is calculated from the following formula:
where is the number of compounds separated, are the retardation factors of each compound sorted in non-descending order, and .
Theoretical considerations
The coefficient lies always in range [0,1] and 0 indicates worst case of separation (all values equal to 0 or 1), value 1 indicates ideal equal-spreading of the spots, for example (0.25,0.5,0.75) for three solutes, or (0.2,0.4,0.6,0.8) for four solutes.
This coefficient was proposed as an alternative to earlier approaches, such as delta-Rf, delta-Rf product or MRF (Multispot Response Function). Besides its stable range, the advantage is a stable distribution as a random variable, regardless of compounds investigated.
In contrast to the similar concept called retention uniformity, is sensitive to values close to 0 or 1, or close to themselves. If two values are not separated, it is equal to 0. For example, the values (0,0.2,0.2,0.3) (two compounds not separated at 0.2 and one at the start ) result in equal to 0, but equal to 0.3609. When some distance from 0 and spots occurs, the value is larger, for example values (0.1,0.2,0.25,0.3) give , .
See also
Chromatographic response function
References