RETENTION VALUES OF SULFONIC-ACIDS AS A FUNCTION OF THE NATURE AND CONCENTRATION OF INORGANIC SALT IN REVERSED-PHASE ION-PAIR LIQUID-CHROMATOGRAPHY

The capacity factors of phenylamine and naphthylamine sulphonic acids in reversed-phase ion-pair liquid chromatography (RP-IPC) with differe nt concentration of inorganic anions were measured. The capacity facto rs of ionic solutes decreases in the order NaF > NaBr >= NaNO3 > Na2SO 4, which is the same as their order of anion retention values in anion ion chromatography. The good linear relationship between logarithm of capacity factors at different inorganic salt eluents were observed. T he effect of salt concentration (C-S) on retention follows an equation based on the Gouy-Chapman model: In k' = A - R(Z(A)/Z(I)) In C-S The absolute value of slopes in RP-IPC is much smaller than the ratio of s olute charge to eluent ion charge in ion chromtagraphy, and increases with the ionic solute charges as well as the retention value of the el uent ions in ion chromatography, but decreses with charge of eluent io ns. The value of intercepts are also related with physico-chemical beh aviors of the ionic solute and eluent ions. The combined effects of sa lt concentration and salt nature on retention values can be described by ln k' = a + b/n(e) ln C-S + c ln t(S)' + d n(e) The salt concentrat ion C-S, and adjusted retention value of salt in ion chromatography (l n t(S)) makes the negative, but the negative (In k' and adjusted reten tion value of salt in charges of sulphonic acids does a positive contr ibution to retention values in RP-IPC.