The capacity factors of 15 aromatic sulfonic acids in reversed-phase ion-pair liquid chromatog. (RP-IPC) with acetonitrile/water and methanol/water containing ion-pair reagent tetrabutylammonium iodide were measured. The linear regression between the ln k' values and methanol, acetonitrile concns. according to equation ln k' = a + Ccb was carried out. Good linear relations of the ln k' values, the parameters a and C with acetonitrile as organic modifier vs. those with methanol as organic modifier were obtained, which mean that there is no significant difference in acetonitrile and methanol affecting the selectivity; the acetonitrile has a stronger eluent strength than methanol. The combined effect of organic modifier and ion-pair reagent concentration on retention values can be expressed by the equation ln k' = A + B ln cp + Ccb in a suitable range of ion-pair reagent concentration A crit. value the pos. effect of ion-pair reagent concentration on retention is the neg. effect of organic modifier concentration on retention was obtained.

Key words: WATER, METHANOL, ACETONITRILE, RETENTION-VALUE, ION PAIR LIQUID CHROMATOGRAPHY, AMINOBENZENESULFONIC ACID, NAPHTHYLAMINE SULFONIC ACID