Several approaches can be used for the prediction of the optimum eluen
t composition in RP-HPLC, but only a few are known that use the struct
ure of the solute. The latest release of the computer program EluEx, v
ersion 3.0, was developed to help the chromatographer in practical wor
k. The program is based on the prediction of the pK(2) and log P (loga
rithm of 1-octanol-water partition coefficient) values of the solutes.
The first eluent suggestion can be done without any preliminary pract
ical work, based on the structural formulae of the solutes. In our exp
erience, two or three experiments are usually sufficient to determine
the optimized binary conditions. The surface heterogeneity and the div
ersity of RP columns, such as the effect of silanol interaction, can b
e handled by the program only to a limited extent. If the difference i
n hydrophobicity between two compounds is small, the elution order can
not be predicted properly in all instances. The same is true for some
isomers, e.g., diastereomers. In this paper, the results of applying t
he program to some neutral, acidic and basic solutes are summarized.