HPLC ANALYSIS OF BASIC ORGANIC-COMPOUNDS IN A MULTICOMPONENT ION-INTERACTION SYSTEM - A MECHANISTIC STUDY

Reversed-phase HPLC separations of basic compounds have been optimized by use of mobile phases containing 1,8-diaminooctane (DAO) as amine m odifier and heptanesulfonate as counter-ion. Such studies have demonst rated the high resolution and selectivity of this chromatographic syst em compared with mobile phases prepared with the more widely used prim ary amines. With the aim of clarifying the retention mechanism involve d, three sets of compounds with different structures and properties we re analyzed: sulfamidics and trimethoprim, aromatic diamines and amino phenols, and a standard mixture of lipophilic basic drugs. The conditi ons investigated were: diaminoalkane modifier concentration, diaminoal kane modifier alkyl-chain length, nature and concentration of the coun ter-ion, pH of the mobile phase, concentration of the organic modifier , and the nature of the stationary phase as characterized by percentag e carbon loading. Analysis of chromatographic behavior as a function o f the chromatographic conditions has enabled the proposal of a mechani sm of retention of the three classes of compounds.