An indexing scheme for optimizing the choice of biphasic systems for CCC

Homologous series of N-alkylbenzamides, N-acylcytosines and N-acylcytidines are introduced as standards for comparing the relative polarity of solvent systems employed in countercurrent chromatography (CCC). A solvent system equipollent index, E, is defined as the fractional carbon chain length of t he standard which would have a partition coefficient of unity in the solven t system. Alkylbenzamide indices, E-B, are suitable to characterize nonpola r to moderately polar systems while more polar systems can be characterized by acylcytosine, E-CS, and acylcytidine, E-CD, indices. Both organic/aqueo us and organic/organic bi-phasic systems can be compared. Disparate systems with the same index are defined as synonymous systems wit h respect to the standard. As a result of different solvent selectivity, sy nonymous systems are expected to exhibit different solubility and retention behavior toward chromatographically similar solutes, which may enhance sol ute separation in some of the systems. Correlation of estimated octanol/wat er partition coefficients with E values aids the choice of solvent systems for compounds of known structure. Solutes with unknown structures can be co mpared directly with equipollent standards using other chromatographic meth ods.