Widening of the elution window in micellar electrokinetic chromatography with cationic surfactants - I. Selection of surfactant, variation of pH and addition of organic modifiers or inorganic metal salts

Although cationic surfactants offer complementary selectivity to anionic su rfactants, most of the work in micellar electrokinetic chromatography (MEKC ) has been done with anionic surfactants, due to the fact that the migratio n window is unfavorably much narrower with cationic surfactants than with a nionic surfactants. In order to overcome the inherent disadvantages of cati onic surfactants, methods are discussed and investigated that make it possi ble to widen the migration window. These methods include variation of the l ength of the alkyl chain of the surfactant employed, variation of the pH, a ddition of organic solvents and other organic modifiers, increase of the io nic strength of the separation electrolyte, and addition of inorganic salts with divalent metal ions (CaCl2, BaCl2). It will be shown that addition of inorganic salts with divalent metal ions can be successfully used in order to improve the migration window in MEKC with cationic surfactant Impact of the modifiers employed on retention of neutral and acidic solutes and on t he efficiency of the separation system is investigated. (C) 1999 Elsevier S cience B.V. All rights reserved.