The coefficient lies always in range and 0 indicates worst case of separation (all Rf 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,
Rd is sensitive to
Rf values close to 0 or 1, or close to themselves. If two values are not separated, it is equal to 0. For example, the
Rf values (0,0.2,0.2,0.3) (two compounds not separated at 0.2 and one at the start ) result in
RD equal to 0, but
RU equal to 0.3609. When some distance from 0 and spots occurs, the value is larger, for example
Rf values (0.1,0.2,0.25,0.3) give
RD = 0.4835,
RU = 0.4066. == See also ==