In thin layer chromatography, retention uniformity (denoted ) is a quantitative measurement of equal-spreading of the spots on the chromatographic plate and is one of the chromatographic response functions.
Formula Retention uniformity is calculated from the following formula:
where is the number of compounds separated and are the retention factors of each compound , sorted in non-descending order.
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 (separation response), (performance index) or (informational entropy). 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 distance, is insensitive to values close to 0 or 1, or close to themselves. If two values are not separated, it still indicates some uniformity of chromatographic system. 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 0.3609.
See also
Chromatographic response function
References
Komsta Ł., Markowski W., Misztal G., A proposal for new RF equal-spread criteria with stable distribution parameters as a random variable. J. Planar Chromatogr. 2007 (20) 27-37.